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/chat/AskButton.tsx

@@ -0,0 +1,32 @@
+"use client";
+
+import { useRouter } from "next/navigation";
+
+import { ChatIcon } from "@/components/icons";
+import { Button } from "@/components/ui";
+import { setChatSeed, type ChatSeed } from "@/lib/chat-seed";
+import { useI18n } from "@/lib/i18n";
+import { cn } from "@/lib/utils";
+
+/**
+ * "Ask a question" entry point for results screens: hands the compact result
+ * summary to the chat (sessionStorage, one-shot) and opens it.
+ */
+export function AskButton({ seed, className }: { seed: ChatSeed; className?: string }) {
+  const { t } = useI18n();
+  const router = useRouter();
+
+  return (
+    <Button
+      variant="secondary"
+      className={cn("touch-target", className)}
+      onClick={() => {
+        setChatSeed(seed);
+        router.push("/chat");
+      }}
+    >
+      <ChatIcon className="size-4" />
+      {t("chat.askQuestion")}
+    </Button>
+  );
+}