Chat mode, phase 1: grounded streaming chat over your notes

Entry points (no sixth tab): Ask in the Library header (desktop button,
phone icon), Ask about this deck in the deck menu, Ask a question on
study/homework results (compact result travels as context), and a Chat
row in the desktop sidebar. Phones get a full-screen route with back +
New chat; the tab bar steps aside.

- Client-side retrieval: chunk scoped decks (~800 tokens), BM25 against
  the question + recent turns, top chunks under ~7k tokens, each
  labelled with deck + section. Notes come from the deck's stored
  sourceText (already kept for Regenerate); decks without it fall back
  to generated content and the UI says so.
- Stateless server: /api/chat validates against the CHAT_MODELS
  allowlist, trims the history to ~6k tokens, caps context at ~9k and
  streams token/thinking/done/error NDJSON. /api/chat/extract reduces
  attachments to text through the existing vision step.
- UI: user bubbles + full-width assistant text, streaming with stop,
  auto-scroll that pauses with a jump-to-bottom button, safe markdown
  (React nodes, no HTML injection; KaTeX dynamically imported only when
  a message has math), Thinking row for reasoning, copy/regenerate/
  edit-and-resend, model + context pickers (last model remembered),
  composer with visualViewport keyboard handling, safe-area, 16px
  textarea, Enter-to-send on desktop.
- Usage-limit failures keep the draft and show the shared message with
  Settings/Ollama actions; stopping maps the reader abort to a clean
  stopped state; offline disables sending with a reason.
- Settings: Keep notes text for chat toggle; deck menu: Delete notes
  text. RATE_LIMIT_CHAT + CHAT_MODELS in .env.example and README.
- Tests: chat suite (63 checks, stub Ollama) wired into run-all.
  Full set: 12/12 suites, 487 checks. SW -> freezmo-v32.

Also: tests/model-compare.mjs (diagnostic) benchmarks two models on the
same notes (latency, repair rounds, activity types) so the gpt-oss vs
gemma default can be decided on numbers; defaults unchanged.

components/icons.tsx

@@ -316,6 +316,70 @@ export function AddToHomeIcon({ className }: IconProps) {
   );
 }
 
+/* --- Chat --------------------------------------------------------------- */
+
+export function ChatIcon({ className }: IconProps) {
+  return (
+    <Svg className={className}>
+      <path d="M20 12a7.5 7.5 0 0 1-7.5 7.5H8.2L4 22v-4.6A7.5 7.5 0 0 1 12.5 4.5 7.5 7.5 0 0 1 20 12Z" />
+      <path d="M9 10.5h7M9 13.8h4.5" />
+    </Svg>
+  );
+}
+
+export function SendIcon({ className }: IconProps) {
+  return (
+    <Svg className={className}>
+      <path d="M12 19V5" />
+      <path d="m6 11 6-6 6 6" />
+    </Svg>
+  );
+}
+
+export function StopIcon({ className }: IconProps) {
+  return (
+    <Svg className={className}>
+      <rect x="7" y="7" width="10" height="10" rx="2" fill="currentColor" stroke="none" />
+    </Svg>
+  );
+}
+
+export function CopyIcon({ className }: IconProps) {
+  return (
+    <Svg className={className}>
+      <rect x="9" y="9" width="11" height="11" rx="2.5" />
+      <path d="M5.5 15H5a1 1 0 0 1-1-1V5a1 1 0 0 1 1-1h9a1 1 0 0 1 1 1v.5" />
+    </Svg>
+  );
+}
+
+export function PaperclipIcon({ className }: IconProps) {
+  return (
+    <Svg className={className}>
+      <path d="m20 11.5-7.8 7.8a5 5 0 0 1-7-7l8.3-8.3a3.3 3.3 0 0 1 4.7 4.7l-8.3 8.3a1.7 1.7 0 0 1-2.4-2.4l7.4-7.4" />
+    </Svg>
+  );
+}
+
+export function PencilIcon({ className }: IconProps) {
+  return (
+    <Svg className={className}>
+      <path d="M4 20h4.2L20 8.2a2.1 2.1 0 0 0-3-3L5.2 17 4 20Z" />
+      <path d="m14.5 6.7 2.8 2.8" />
+    </Svg>
+  );
+}
+
+export function HistoryIcon({ className }: IconProps) {
+  return (
+    <Svg className={className}>
+      <path d="M4.5 12a7.5 7.5 0 1 1 2.2 5.3" />
+      <path d="M4.5 12H2m2.5 0 2.3-2.3M4.5 12l2.3 2.3" />
+      <path d="M12 8.5V12l2.4 1.6" />
+    </Svg>
+  );
+}
+
 export function ChromeIcon({ className }: IconProps) {
   return (
     <Svg className={className}>