feat(desktop): Feed + Wallet sections (v2.2.0-alpha6)

Desktop client reaches full feature parity with mobile for the two
heaviest sections. Contacts + Devices screen + polish pass remain for
rc1.

Feed section (src/sections/feed/ + src/lib/feed.ts):
  * Left pane — FeedTabs: For You / Following / Trending 24h + a
    hashtag input that promotes to a tab on Enter; breadcrumb back-
    navigation when you drill into an author wall or hashtag.
  * Right pane — FeedPane: two sub-columns. Scrollable post list
    (truncated body, likes/views/hashtags footer, active highlight)
    + PostDetail with full body, hashtag links (click → hashtag tab),
    inline attachment image, like/unlike button, Delete (if mine).
    On-mount side-effects: bumpView + fetchStats for liked-by-me.
  * ComposeModal — new-post dialog. Ctrl/Cmd+N opens it; Ctrl+Enter
    submits. Byte counter against 4000 limit, live hashtag preview.
    Uses publishAndCommit (server-side image scrub happens when
    attachments land in rc1).
  * lib/feed.ts — full mirror of mobile's feed.ts:
    fetchForYou/Timeline/Trending/Author/Hashtag/Post/Stats,
    bumpView, like/unlike/delete/follow/unfollow, publishPost +
    publishAndCommit + buildCreatePostTx. Uses window.crypto.subtle
    for SHA-256 (no expo-crypto dep). Same canonical-bytes as mobile.

Wallet section (src/sections/wallet/ + new bits in src/lib/api.ts):
  * WalletOverview (left): account card (balance + shortened pub +
    Send/Receive/Refresh) and transaction history grouped by row.
    Amount colour-codes by direction; pretty tx-type labels.
  * WalletDetailPane (right): selected tx — big signed amount,
    2-column key/value grid (id, from, to, amount, fee, time, block,
    gas), collapsible JSON payload + payload_hex fallback. Mirror of
    mobile /tx/[id] layout.
  * SendModal — transfer tx with @username / DC-address / hex pub
    resolution via resolveAccount. Balance + fee preview; refuses
    self-transfer (would roundtrip through mempool for no reason).
  * ReceiveModal — pub + Copy button. QR in rc1 once we pull in a
    qrcode lib.
  * lib/api.ts: TxRow + TxDetail types, getTxHistory, getTxDetail,
    resolveAccount (handles hex/@username/DC-address).

Store adds feedTab + feedSelectedPost + walletSel so selection state
survives section-switches. FeedTab discriminated union covers the
hashtag + author sub-states so breadcrumbs know what to render.

Typecheck + renderer build both pass. Node API used as-is — no
server changes in this release.

desktop/src/sections/wallet/SendModal.tsx

@@ -0,0 +1,219 @@
+// SendModal — a focused little dialog for Transfer tx's. Accepts a
+// hex pub, DC-address, or @username and resolves to the Ed25519 pub
+// before submitting. Validates amount against balance + min fee.
+
+import React, { useEffect, useMemo, useState } from 'react';
+import { useStore } from '@/lib/store';
+import { getBalance, resolveAccount } from '@/lib/api';
+import { buildTransferTx, submitTx, humanizeTxError } from '@/lib/tx';
+
+const MIN_FEE_UT = 1_000;
+
+function parseAmountT(s: string): number | null {
+  const n = parseFloat(s);
+  if (!Number.isFinite(n) || n <= 0) return null;
+  return Math.round(n * 1_000_000);
+}
+
+export function SendModal({
+  onClose, onSent,
+}: {
+  onClose: () => void;
+  onSent: () => void;
+}): React.ReactElement {
+  const keyFile = useStore(s => s.keyFile);
+
+  const [toInput, setToInput] = useState('');
+  const [amount,  setAmount]  = useState('');
+  const [memo,    setMemo]    = useState('');
+  const [busy,    setBusy]    = useState(false);
+  const [err,     setErr]     = useState<string | null>(null);
+  const [balance, setBalance] = useState<number | null>(null);
+
+  useEffect(() => {
+    if (!keyFile) return;
+    getBalance(keyFile.pub_key).then(setBalance).catch(() => setBalance(null));
+  }, [keyFile]);
+
+  const amountUT = useMemo(() => parseAmountT(amount), [amount]);
+  const totalUT  = amountUT === null ? null : amountUT + MIN_FEE_UT;
+
+  const canSend = !!keyFile && !busy && amountUT !== null
+                && balance !== null && totalUT !== null && balance >= totalUT
+                && toInput.trim().length > 0;
+
+  const submit = async () => {
+    if (!keyFile || !canSend || amountUT === null) return;
+    setBusy(true); setErr(null);
+    try {
+      const to = await resolveAccount(toInput);
+      if (!to) throw new Error('Can\'t resolve recipient');
+      if (to === keyFile.pub_key) throw new Error('Refusing self-transfer');
+      const tx = buildTransferTx({
+        from:    keyFile.pub_key,
+        to,
+        amount:  amountUT,
+        fee:     MIN_FEE_UT,
+        privKey: keyFile.priv_key,
+        memo:    memo.trim() || undefined,
+      });
+      await submitTx(tx);
+      onSent();
+      onClose();
+    } catch (e) {
+      setErr(humanizeTxError(e));
+    } finally {
+      setBusy(false);
+    }
+  };
+
+  return (
+    <Backdrop onClose={busy ? () => {} : onClose}>
+      <div style={{
+        width: '100%', maxWidth: 460, padding: 20, borderRadius: 16,
+        background: '#0a0a0a', border: '1px solid #1f1f1f',
+      }}>
+        <Header title="Send" onClose={onClose} busy={busy} />
+        <div style={{ display: 'flex', flexDirection: 'column', gap: 12 }}>
+          <Field label="To" hint="@username, DC-address or hex pubkey">
+            <input
+              value={toInput}
+              onChange={e => setToInput(e.target.value)}
+              placeholder="@alice or DC… or <hex>"
+              spellCheck={false}
+              autoFocus
+              style={inputStyle}
+            />
+          </Field>
+          <Field label="Amount (T)">
+            <input
+              value={amount}
+              onChange={e => setAmount(e.target.value)}
+              placeholder="0.0"
+              inputMode="decimal"
+              style={inputStyle}
+            />
+            <div style={{ color: '#6a6a6a', fontSize: 11, marginTop: 4 }}>
+              Balance: {balance === null ? '…' : `${(balance / 1_000_000).toLocaleString(undefined, { maximumFractionDigits: 6 })} T`}
+              {amountUT !== null && (
+                <> · Fee: {(MIN_FEE_UT / 1_000_000).toFixed(6)} T</>
+              )}
+            </div>
+          </Field>
+          <Field label="Memo (optional)">
+            <input
+              value={memo}
+              onChange={e => setMemo(e.target.value)}
+              placeholder="Invoice #42"
+              style={inputStyle}
+            />
+          </Field>
+        </div>
+
+        {err && (
+          <div style={{
+            marginTop: 12, padding: 10, borderRadius: 8,
+            background: '#2a1414', color: '#ff9b9b', fontSize: 12,
+          }}>{err}</div>
+        )}
+
+        <div style={{
+          marginTop: 16, display: 'flex', justifyContent: 'flex-end', gap: 10,
+        }}>
+          <button
+            onClick={onClose}
+            disabled={busy}
+            style={secondaryBtnStyle(busy)}
+          >Cancel</button>
+          <button
+            onClick={submit}
+            disabled={!canSend}
+            style={primaryBtnStyle(!canSend)}
+          >{busy ? '…' : 'Send'}</button>
+        </div>
+      </div>
+    </Backdrop>
+  );
+}
+
+// ─── Shared modal primitives used by Send/Receive ────────────────────────
+
+function Backdrop({ children, onClose }: { children: React.ReactNode; onClose: () => void }) {
+  return (
+    <div
+      onClick={onClose}
+      style={{
+        position: 'fixed', inset: 0, zIndex: 20,
+        background: 'rgba(0,0,0,0.7)',
+        display: 'flex', alignItems: 'center', justifyContent: 'center',
+        padding: 24,
+      }}
+    >
+      <div onClick={e => e.stopPropagation()} style={{ width: '100%', display: 'flex', justifyContent: 'center' }}>
+        {children}
+      </div>
+    </div>
+  );
+}
+
+function Header({ title, onClose, busy }: {
+  title: string; onClose: () => void; busy: boolean;
+}) {
+  return (
+    <div style={{
+      display: 'flex', alignItems: 'center', justifyContent: 'space-between',
+      marginBottom: 14,
+    }}>
+      <div style={{ color: '#fff', fontSize: 16, fontWeight: 700 }}>{title}</div>
+      <button
+        onClick={onClose}
+        disabled={busy}
+        style={{
+          background: 'transparent', border: 'none',
+          color: '#8b8b8b', fontSize: 20, cursor: 'pointer',
+        }}
+      >×</button>
+    </div>
+  );
+}
+
+function Field({ label, hint, children }: {
+  label: string; hint?: string; children: React.ReactNode;
+}) {
+  return (
+    <div>
+      <div style={{
+        color: '#8b8b8b', fontSize: 11, fontWeight: 700,
+        letterSpacing: 1, textTransform: 'uppercase', marginBottom: 6,
+      }}>{label}</div>
+      {children}
+      {hint && (
+        <div style={{ color: '#6a6a6a', fontSize: 11, marginTop: 4 }}>{hint}</div>
+      )}
+    </div>
+  );
+}
+
+const inputStyle: React.CSSProperties = {
+  width: '100%', boxSizing: 'border-box',
+  background: '#000', border: '1px solid #1f1f1f',
+  borderRadius: 8, padding: '10px 12px',
+  color: '#fff', fontSize: 13, fontFamily: 'inherit',
+  outline: 'none',
+};
+
+const primaryBtnStyle = (disabled: boolean): React.CSSProperties => ({
+  padding: '9px 18px', borderRadius: 999, border: 'none',
+  background: '#1d9bf0', color: '#fff',
+  fontSize: 13, fontWeight: 700,
+  cursor: disabled ? 'default' : 'pointer',
+  opacity: disabled ? 0.5 : 1,
+});
+const secondaryBtnStyle = (disabled: boolean): React.CSSProperties => ({
+  padding: '9px 14px', borderRadius: 999,
+  background: 'transparent', border: '1px solid #1f1f1f',
+  color: '#8b8b8b', fontSize: 13, fontWeight: 700,
+  cursor: disabled ? 'default' : 'pointer',
+});
+
+export { Backdrop, Header, Field, inputStyle, primaryBtnStyle, secondaryBtnStyle };