feat(cockpit): approval preview — command/diff above Approve/Reject (W1)

Remote one-tap approval was blind (you'd tap Approve without seeing Claude wants
to run `rm -rf` or rewrite a config). The pending tool's actual command / diff now
renders above the approval bar, on every attached device, riding the same broadcast
+ late-joiner rails as the existing `gate` field.

- src/http/approval-preview.ts (new, pure, never-throws): deriveApprovalPreview —
  Bash → command; Edit/Write/MultiEdit/NotebookEdit → a synthetic DiffFile; else null.
  Every line sanitized via sanitizeField (strips control/ANSI); caps 40 lines /
  200 chars/line / 4KB (security limits, UTF-8-safe byte clamp).
- src/types.ts: additive optional `preview?: ApprovalPreview` on the status
  ServerMessage + handleHookEvent (older clients ignore it).
- src/server.ts /hook/permission: derive preview from tool_input, store on the
  PendingApproval entry, re-send to late joiners exactly like `gate`.
- manager.ts threads it; public/tabs.ts renderApprovalPreview (command → <pre>
  textContent; diff → reused innerHTML-free renderDiffFile). Unknown tools /
  plan gates fall back to today's name-only bar.

Attacker-influenced tool input → rendered via textContent/diff-renderer only,
never innerHTML. Verified independently: typecheck + build:web clean, 1692 pass.

test/manager.test.ts

@@ -799,6 +799,39 @@ describe('handleHookEvent — gate broadcast (B4)', () => {
   });
 });
 
+// ── handleHookEvent — W1 preview broadcast ────────────────────────────────────
+describe('handleHookEvent — preview broadcast (W1)', () => {
+  it('puts the preview arg on the broadcast status frame (deep equal)', () => {
+    const mgr = createSessionManager(CFG);
+    const a = createMockWs();
+    const b = createMockWs();
+    const s = mgr.handleAttach(a, null, DIMS, 1_000);
+    mgr.handleAttach(b, s.meta.id, DIMS, 2_000);
+    a.sent.length = 0;
+    b.sent.length = 0;
+
+    const preview = { kind: 'command', text: 'ls -la' } as const;
+    mgr.handleHookEvent(s.meta.id, 'waiting', 'Bash', true, 'tool', undefined, undefined, preview);
+
+    for (const ws of [a, b]) {
+      const status = parseSent(ws).find((m) => m.type === 'status');
+      expect(status.preview).toEqual(preview);
+    }
+  });
+
+  it('omits the preview key when no preview is supplied', () => {
+    const mgr = createSessionManager(CFG);
+    const ws = createMockWs();
+    const s = mgr.handleAttach(ws, null, DIMS, 1_000);
+    ws.sent.length = 0;
+
+    mgr.handleHookEvent(s.meta.id, 'waiting', 'Bash', true, 'tool');
+
+    const status = parseSent(ws).find((m) => m.type === 'status');
+    expect(status).not.toHaveProperty('preview');
+  });
+});
+
 // ── handleStatusLine (B2 telemetry) ───────────────────────────────────────────
 describe('handleStatusLine', () => {
   it('stores telemetry on the session and broadcasts it to all clients', () => {