UI iteration 1: app shell + full LaTeX pipeline

Layout:
- Home = knowledge-graph placeholder (main view) with new-session input
  docked below; session list moved out of home into a hamburger drawer
- SessionDrawer: slide-over session navigation (backdrop/ESC close, active
  highlight, fetches /api/chats on open) on both home and chat headers
- Chat header loses the back button — the drawer is the navigation

Math (inline $ was silently not rendering):
- @streamdown/math defaults singleDollarTextMath:false — now
  createMathPlugin({ singleDollarTextMath: true }) in message + reasoning
- katex.min.css imported in layout (streamdown does not inject plugin
  styles; display math only looked right via browser MathML fallback)
- QuizCard/AnsweredCard route question/options/explanation through
  MessageResponse; user chat bubbles render markdown+math too
- Currency hazard: micromark-extension-math@3.1 lacks pandoc's
  closing-digit rule, so bare '$5 and $10' parses as math — defense is at
  the source: system prompt now instructs escaped \$5 / 'USD' for money

Hydration fix (React #418):
- QuizCard shuffled options with Math.random() — server/client orders
  diverged. shuffleOptions now takes an injectable RNG; QuizCard passes
  seededRandom(toolCallId) (mulberry32/FNV-1a in question-core). Same
  question → same stable order across reloads; still varies per question.

Tests: 53 pass (5 new math-rendering pins incl. fenced-vs-one-line $$
behavior and the escaped-currency contract). tsc + next build clean.
Verified live in browser: inline/display math in text + cards, drawer
open/navigate/active-highlight/ESC, no console errors, no font 404s.

src/agent/system-prompt.md

@@ -182,6 +182,8 @@ Whenever math notation is involved — explanations, questions, quiz options and
 
 If LaTeX can be used, it should be. Write $f(x) = x^2$, not `f(x) = x^2`. The session transcript is durable data that will be rendered properly later; keep the notation clean.
 
+One hazard: a bare `$` starts math. NEVER write currency as `$5` — write `\$5` (escaped) or `5 USD`. This applies to quiz questions, options, and explanations too.
+
 ## Session shape — one more thing
 
 Every session you run produces the artifact from which the learner's knowledge graph is built: the quiz outcomes, the dependency map, the propositions you teach. Teach in clean, explicit units — each node stated crisply (e.g. "**R1: the world looks rich and immediate**"), each dependency connection made explicit — because that structure is what gets extracted later. Vague, hedged, mushy node statements can't be extracted; crisp ones can. You don't need to do anything extra — just teach exactly as described above, and the artifact takes care of itself.