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/homework/HomeworkCheckResult.tsx

@@ -3,6 +3,7 @@
 import { useState } from "react";
 
 import { Button } from "@/components/ui";
+import { AskButton } from "@/components/chat/AskButton";
 import { useI18n } from "@/lib/i18n";
 import type { HomeworkCheckRecord } from "@/lib/schemas";
 
@@ -97,6 +98,27 @@ export function HomeworkCheckResult({
       </article>
 
       <div className="flex flex-wrap items-start gap-2">
+        <AskButton
+          seed={{
+            label: record.title,
+            text: [
+              `${t("chat.seedAssignment")}:`,
+              record.sourceText,
+              "",
+              `${t("chat.seedAttempt")}:`,
+              record.attempt ?? "",
+              "",
+              `${t("chat.seedVerdict")}:`,
+              record.verdict,
+              ...(record.wrong.length > 0
+                ? ["", `${t("chat.seedToFix")}:`, ...record.wrong.map((entry) => `- ${entry.issue}: ${entry.why} → ${entry.fix}`)]
+                : []),
+              "",
+              `${t("chat.seedCorrected")}:`,
+              corrected,
+            ].join("\n"),
+          }}
+        />
         <Button variant="secondary" className="touch-target" onClick={onAgain} loading={againLoading}>
           {t("homework.followup.redo")}
         </Button>