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.

lib/settings.ts

@@ -24,11 +24,17 @@ export type BrowserSettings = {
   haptics: boolean;
   /** How many answers count as a finished day in the Library/stats. */
   dailyGoal: number;
+  /**
+   * Whether chat may ground its answers in the deck's stored notes text
+   * (`sourceText`). On by default; off means chat only sees the generated
+   * study content.
+   */
+  chatNotes: boolean;
 };
 
 const DEFAULT_GOAL = 20;
 
-const EMPTY: BrowserSettings = { apiKey: "", haptics: true, dailyGoal: DEFAULT_GOAL };
+const EMPTY: BrowserSettings = { apiKey: "", haptics: true, dailyGoal: DEFAULT_GOAL, chatNotes: true };
 
 let cached: BrowserSettings | null = null;
 const listeners = new Set<() => void>();
@@ -44,6 +50,7 @@ function read(): BrowserSettings {
       apiKey: typeof parsed.apiKey === "string" ? parsed.apiKey.slice(0, 512) : "",
       haptics: parsed.haptics !== false,
       dailyGoal: Number.isFinite(goal) ? Math.min(500, Math.max(1, goal)) : DEFAULT_GOAL,
+      chatNotes: parsed.chatNotes !== false,
     };
   } catch {
     return EMPTY;
@@ -53,10 +60,10 @@ function read(): BrowserSettings {
 function write(next: BrowserSettings): void {
   cached = next;
   try {
-    if (next.apiKey || next.haptics === false || next.dailyGoal !== DEFAULT_GOAL) {
+    if (next.apiKey || next.haptics === false || next.dailyGoal !== DEFAULT_GOAL || next.chatNotes === false) {
       window.localStorage.setItem(
         STORAGE_KEY,
-        JSON.stringify({ apiKey: next.apiKey, haptics: next.haptics, dailyGoal: next.dailyGoal }),
+        JSON.stringify({ apiKey: next.apiKey, haptics: next.haptics, dailyGoal: next.dailyGoal, chatNotes: next.chatNotes }),
       );
     } else {
       window.localStorage.removeItem(STORAGE_KEY);