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.

lib/schemas.ts

@@ -339,3 +339,52 @@ export const srsRecordSchema = z.object({
   lastCorrect: z.boolean(),
 });
 export type SrsRecord = z.infer<typeof srsRecordSchema>;
+
+/* ------------------------------------------------------------------ */
+/* Chat (history, sources, scopes)                                     */
+/* ------------------------------------------------------------------ */
+
+export const chatSourceSchema = z.object({
+  deckId: z.string().min(1).max(120),
+  deckTitle: z.string().max(200),
+  section: z.string().max(200),
+});
+export type ChatSource = z.infer<typeof chatSourceSchema>;
+
+export const chatAttachmentSchema = z.object({
+  name: z.string().max(200),
+  kind: z.enum(["photo", "document", "text"]),
+  chars: z.number().int().min(0).max(10_000_000),
+});
+export type ChatAttachment = z.infer<typeof chatAttachmentSchema>;
+
+export const chatMessageSchema = z.object({
+  id: z.string().min(1).max(80),
+  role: z.enum(["user", "assistant"]),
+  content: z.string().max(20_000),
+  thinking: z.string().max(20_000).optional(),
+  model: z.string().max(120).optional(),
+  sources: z.array(chatSourceSchema).max(40).optional(),
+  attachments: z.array(chatAttachmentSchema).max(10).optional(),
+  at: z.number(),
+  error: z.object({ message: z.string().max(2000), kind: z.string().max(40).optional() }).optional(),
+});
+export type ChatMessage = z.infer<typeof chatMessageSchema>;
+
+export const chatScopeSchema = z.discriminatedUnion("kind", [
+  z.object({ kind: z.literal("all") }),
+  z.object({ kind: z.literal("none") }),
+  z.object({ kind: z.literal("decks"), deckIds: z.array(z.string().max(120)).max(200) }),
+]);
+export type ChatScope = z.infer<typeof chatScopeSchema>;
+
+export const chatConversationSchema = z.object({
+  id: z.string().min(1).max(80),
+  title: z.string().max(200),
+  messages: z.array(chatMessageSchema).max(300),
+  scope: chatScopeSchema,
+  model: z.string().max(120).optional(),
+  createdAt: z.number(),
+  updatedAt: z.number(),
+});
+export type ChatConversation = z.infer<typeof chatConversationSchema>;