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/CopyIconButton.tsx

@@ -0,0 +1,39 @@
+"use client";
+
+import { useState } from "react";
+
+import { CheckCircleIcon, CopyIcon, XCircleIcon } from "@/components/icons";
+import { copyText } from "@/lib/clipboard";
+import { useI18n } from "@/lib/i18n";
+import { cn } from "@/lib/utils";
+
+/** Small square copy control used by chat message actions and code blocks. */
+export function CopyIconButton({ text, className }: { text: string; className?: string }) {
+  const { t } = useI18n();
+  const [state, setState] = useState<"idle" | "copied" | "failed">("idle");
+
+  return (
+    <button
+      type="button"
+      aria-label={t("chat.copy")}
+      title={state === "copied" ? t("chat.copied") : state === "failed" ? t("chat.copyFailed") : t("chat.copy")}
+      onClick={async () => {
+        const ok = await copyText(text);
+        setState(ok ? "copied" : "failed");
+        window.setTimeout(() => setState("idle"), 1800);
+      }}
+      className={cn(
+        "grid size-9 shrink-0 place-items-center rounded-xl border border-[var(--glass-border)] bg-[var(--surface-strong)] text-[var(--text-muted)] transition hover:bg-[var(--hover)] hover:text-[var(--text)]",
+        className,
+      )}
+    >
+      {state === "copied" ? (
+        <CheckCircleIcon className="size-4 text-emerald-500" />
+      ) : state === "failed" ? (
+        <XCircleIcon className="size-4 text-rose-500" />
+      ) : (
+        <CopyIcon className="size-4" />
+      )}
+    </button>
+  );
+}