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/SettingsDialog.tsx

@@ -391,6 +391,17 @@ export function SettingsDialog({
                           />
                         </button>
                       </div>
+
+                      {/* chat grounding: may chat read the notes text? */}
+                      <ToggleRow
+                        label={t("settings.chatNotes")}
+                        note={t("settings.chatNotesNote")}
+                        checked={settings.chatNotes}
+                        onChange={() => {
+                          saveSettings({ chatNotes: !settings.chatNotes });
+                          haptic("toggle");
+                        }}
+                      />
                     </section>
 
                     {/* ------------------------------------------- data & sync */}
@@ -709,6 +720,16 @@ export function SettingsDialog({
                   ) : null}
                 </section>
 
+                {/* ------------------------------------------- chat grounding */}
+                <section className="mb-4 rounded-2xl border border-[var(--hairline)] bg-[var(--surface-sunken)] p-3">
+                  <ToggleRow
+                    label={t("settings.chatNotes")}
+                    note={t("settings.chatNotesNote")}
+                    checked={settings.chatNotes}
+                    onChange={() => saveSettings({ chatNotes: !settings.chatNotes })}
+                  />
+                </section>
+
                 {/* ------------------------------------------- data & sync */}
                 <LearningSection />
                 <DataSection />
@@ -947,3 +968,44 @@ function ModelRow({
     </div>
   );
 }
+
+/** Boolean toggle row used by the chat-grounding setting. */
+function ToggleRow({
+  label,
+  note,
+  checked,
+  onChange,
+}: {
+  label: string;
+  note: string;
+  checked: boolean;
+  onChange: () => void;
+}) {
+  return (
+    <div className="flex items-center justify-between gap-3 border-t border-[var(--hairline-soft)] pt-3">
+      <span className="min-w-0">
+        <span className="block text-[13px] font-semibold text-[var(--text)]">{label}</span>
+        <span className="block text-[11.5px] leading-snug text-[var(--text-subtle)]">{note}</span>
+      </span>
+      <button
+        type="button"
+        role="switch"
+        aria-checked={checked}
+        aria-label={label}
+        onClick={onChange}
+        className={cn(
+          "touch-target relative h-7 w-12 shrink-0 rounded-full border transition-colors",
+          checked ? "grad-ice border-transparent" : "border-[var(--hairline)] bg-[var(--surface-sunken)]",
+        )}
+      >
+        <span
+          aria-hidden
+          className={cn(
+            "absolute top-1/2 size-5 -translate-y-1/2 rounded-full bg-white shadow transition-[left] duration-200",
+            checked ? "left-6" : "left-0.5",
+          )}
+        />
+      </button>
+    </div>
+  );
+}