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.

package-lock.json

@@ -11,6 +11,7 @@
         "canvas-confetti": "^1.9.4",
         "framer-motion": "^12.23.24",
         "jszip": "^3.10.2",
+        "katex": "^0.19.0",
         "mammoth": "^1.13.0",
         "next": "15.5.27",
         "pdfjs-dist": "^6.4.299",
@@ -2914,6 +2915,15 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/commander": {
+      "version": "15.0.0",
+      "resolved": "https://registry.npmjs.org/commander/-/commander-15.0.0.tgz",
+      "integrity": "sha512-z67u4ZhzCL/Tydu1lJARtEZYWbWaN7oYLHbsuzocr6y4N6WZAagG3RQ4FW61V1/0+jImpj293XfrcYnd1qxtPg==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=22.12.0"
+      }
+    },
     "node_modules/concat-map": {
       "version": "0.0.1",
       "resolved": "https://registry.npmjs.org/concat-map/-/concat-map-0.0.1.tgz",
@@ -4881,6 +4891,22 @@
         "safe-buffer": "^5.0.1"
       }
     },
+    "node_modules/katex": {
+      "version": "0.19.0",
+      "resolved": "https://registry.npmjs.org/katex/-/katex-0.19.0.tgz",
+      "integrity": "sha512-v6Tznz3zJ7u3niRCoDTsumM2+HA2XXcCu+WAacCeHD2z3p9A9Ks987o5FzfTGBN0e8A0vjEgIDvLbICrXpdw/Q==",
+      "funding": [
+        "https://opencollective.com/katex",
+        "https://github.com/sponsors/katex"
+      ],
+      "license": "MIT",
+      "dependencies": {
+        "commander": "^15.0.0"
+      },
+      "bin": {
+        "katex": "cli.js"
+      }
+    },
     "node_modules/keyv": {
       "version": "4.5.4",
       "resolved": "https://registry.npmjs.org/keyv/-/keyv-4.5.4.tgz",