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/i18n-dict.ts

@@ -160,7 +160,7 @@ const en: Record<string, string> = {
   "settings.exportAll": "Export all data",
   "settings.exportNote": "Decks, homework, progress and settings — never your API key.",
   "settings.importBackup": "Import backup",
-  "settings.importPreview": "This backup has {decks} decks, {homework} homework results and {folders} folders.",
+  "settings.importPreview": "This backup has {decks} decks, {homework} homework results, {folders} folders and {chats} chats.",
   "settings.importMergeNote": "Merge keeps what's here and adds the backup; matching IDs are replaced.",
   "settings.importReplaceNote": "Replace wipes this browser's data and uses the backup instead.",
   "settings.importMerge": "Merge",
@@ -975,6 +975,18 @@ const en: Record<string, string> = {
   "chat.seedSteps": "Steps",
   "chat.notesDeleted": "Notes text deleted",
   "chat.deleteNotes": "Delete notes text",
+  "chat.history": "Chats",
+  "chat.searchChats": "Search chats",
+  "chat.noResults": "No chats match that search.",
+  "chat.noHistory": "No saved chats yet — ask something and it will appear here.",
+  "chat.untitled": "Untitled chat",
+  "chat.deleteChat": "Delete chat",
+  "chat.deletedChat": "Chat deleted",
+  "chat.toFlashcards": "Turn into flashcards",
+  "chat.saveToNotes": "Save to notes",
+  "chat.savedToNotes": "Saved to {deck}'s notes",
+  "chat.savedToNotesTrimmed": "Saved to {deck}'s notes (trimmed to fit)",
+  "chat.savedFromChat": "Saved from chat",
   "settings.chatNotes": "Keep notes text for chat",
   "settings.chatNotesNote": "Chat answers from the notes you added (stored with each deck). Turn off to use only the generated study content.",
   "server.chatModelNotAllowed": "That chat model is not on the server's allowlist.",
@@ -1080,7 +1092,7 @@ const cs: Record<string, string> = {
   "settings.exportAll": "Exportovat všechna data",
   "settings.exportNote": "Sady, úkoly, pokrok a nastavení — nikdy tvůj API klíč.",
   "settings.importBackup": "Importovat zálohu",
-  "settings.importPreview": "Záloha obsahuje {decks} sad, {homework} výsledků úkolů a {folders} složek.",
+  "settings.importPreview": "Záloha obsahuje {decks} sad, {homework} výsledků úkolů, {folders} složek a {chats} chatů.",
   "settings.importMergeNote": "Sloučení ponechá stávající data a přidá zálohu; stejná ID se nahradí.",
   "settings.importReplaceNote": "Nahrazení smaže data v tomto prohlížeči a použije zálohu.",
   "settings.importMerge": "Sloučit",
@@ -1895,6 +1907,18 @@ const cs: Record<string, string> = {
   "chat.seedSteps": "Postup",
   "chat.notesDeleted": "Text poznámek smazán",
   "chat.deleteNotes": "Smazat text poznámek",
+  "chat.history": "Chaty",
+  "chat.searchChats": "Hledat v chatech",
+  "chat.noResults": "Tomuto hledání nic neodpovídá.",
+  "chat.noHistory": "Zatím žádné uložené chaty — na něco se zeptej a objeví se tady.",
+  "chat.untitled": "Chat bez názvu",
+  "chat.deleteChat": "Smazat chat",
+  "chat.deletedChat": "Chat smazán",
+  "chat.toFlashcards": "Převést na kartičky",
+  "chat.saveToNotes": "Uložit do poznámek",
+  "chat.savedToNotes": "Uloženo do poznámek sady {deck}",
+  "chat.savedToNotesTrimmed": "Uloženo do poznámek sady {deck} (zkráceno, aby se vešlo)",
+  "chat.savedFromChat": "Uloženo z chatu",
   "settings.chatNotes": "Uchovávat text poznámek pro chat",
   "settings.chatNotesNote": "Chat odpovídá z poznámek, které jsi přidal (jsou uložené u každé sady). Vypnutím bude používat jen vygenerovaný obsah.",
   "server.chatModelNotAllowed": "Tento model chatu není v povoleném seznamu serveru.",