Chat mode, phase 2: local history, answer actions, motion polish

- Conversations in a versioned IndexedDB store (freezmo-chat v1, zod
  validated with the same schema backup/sync use, capped at 100 x 300).
  Settled turns persist (question always; answer when produced, partial
  stops included); ?c=<id> keeps reloads on the conversation via
  history.replaceState (no router round-trip mid-chat).
- History UI: desktop column, phone sheet (spring, backdrop, Escape),
  auto titles from the first question, inline rename, delete with an
  Undo toast, diacritic-folding search over titles and message text.
  Scope and model are remembered per conversation; history is readable
  offline.
- Assistant actions: Turn into flashcards (New deck with the answer as
  notes, landing on the options step - deck seed gained step) and Save
  to notes (appends to the single scoped deck, trimmed at 40k).
- Chats travel in the backup export (preview counts them) and in the
  encrypted sync payload; still never the key.
- Motion from lib/motion.ts: message fade-up, sheet springs for the
  model/context/history sheets, 150ms composer height transition, all
  skipped under reduced motion.
- Tests: chat suite 63 -> 89 checks (history, reload, rename/search/
  delete/undo, actions, export, two-device sync round-trip, offline,
  desktop panel). Full set: 12/12 suites, 513 checks. SW -> freezmo-v33.

Also: tests/model-compare.mjs benchmark (diagnostic) for deciding the
default text model on numbers; defaults unchanged.

components/chat/Composer.tsx

@@ -122,7 +122,7 @@ export function Composer({
           rows={1}
           placeholder={t("chat.placeholder")}
           aria-label={t("chat.placeholder")}
-          className="max-h-[180px] min-h-[44px] min-w-0 flex-1 resize-none rounded-2xl border border-[var(--glass-border)] bg-[var(--surface-strong)] px-3.5 py-2.5 text-[16px] leading-relaxed text-[var(--text)] outline-none transition placeholder:text-[var(--text-subtle)] focus:border-accent-400/60"
+          className="max-h-[180px] min-h-[44px] min-w-0 flex-1 resize-none rounded-2xl border border-[var(--glass-border)] bg-[var(--surface-strong)] px-3.5 py-2.5 text-[16px] leading-relaxed text-[var(--text)] outline-none transition-[height,border-color] duration-150 ease-out placeholder:text-[var(--text-subtle)] focus:border-accent-400/60 motion-reduce:transition-none"
         />
 
         {busy ? (