Import cartridge .sav files with verified structure, checksums and clock (Closes #44)

Savegames → Import backup now reads an English Crystal .sav (from an
emulator, a cartridge dump or the 3DS Virtual Console's sav.dat) and
converts it into a native save after a preview.

- world/cartridge-save.ts: picks the copy TryLoadSaveFile would load
  (check values and checksums of the main copy, else the backup), reads
  the saved WRAM block, the numbered boxes, mail backups, Hall of Fame and
  Battle Tower by PRET labels (SRAM, SAVE_BLOCK in the profile, checked by
  check:reference with the SAV constants), engine flags via EngineFlags,
  scenes via MapScenes, and the map's objects and masks.
- Clock: an emulator MBC3 footer plus the time since it was written,
  FixDays/FixTime with wStart*, mapped to the minute and weekday offsets;
  without one, the device's time and the saved wCurDay. Day countdowns
  move with the day difference.
- Refused with the reason: unported maps, the Bug-Catching Contest, a
  Battle Tower challenge, characters outside the naming screen.
- Names keep <PK>/<MN> as ᴾᴷ/ᴹᴺ (one character, one tile); trainer names
  accept the naming screen's alphabet; boxed Eggs validate; native states
  up to 256 kB load (a full PC exceeded 64 kB).
- Tests: the committed debug saves, layout offsets against the symbols,
  backup fallback, clock footers, day counters, refusals, slot session
  and the Savegames flow in Chromium and WebKit.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/PLAN.md

@@ -519,6 +519,15 @@ The numbered sections below keep their full scope. Each one opens with a checkli
 - `PokemonCenterPC.ChooseWhichPCListToUse` picks `PCPC_POSTGAME` from the count, as the original does, so HALL OF FAME appears once a team is recorded. `_HallOfFamePC`, `LoadHOFTeam` and `DisplayHOFMon` show each Pokémon's page with its cry: A shows the next Pokémon, then the next team; Start skips to the next team; B returns to the PC. The original's unreachable "HOF Master!" title (it needs a count of 201) is kept.
 - `tests/reference-hall-of-fame.spec.ts` writes 255 teams (every species, Unown, level 100, the Nidorans, win 200, all eight frames) into the cartridge's SRAM, runs its `_HallOfFamePC`, and compares the tilemap, attributes, graphics and palette with the port's page. `HOF_AnimateFrontpic` is the one routine stubbed: the port shows the picture at rest, without the `ANIM_MON_HOF` animation. `tests/hall-of-fame.test.ts` covers the records, the PC menu with and without them, browsing, and save, reload and migration.
 
+## Implemented: cartridge save import (board #44)
+
+- `world/cartridge-save.ts` converts a 32 KiB English Crystal `.sav` (optionally followed by a 44- or 48-byte emulator clock footer, or the Virtual Console's 16 bytes, which are not read) into a version-3 native save. Every SRAM and WRAM address it reads is keyed by its PRET label in `profile.ts` (`SRAM`, `SAVE_BLOCK`) and checked by `npm run check:reference`, like its PRET constants (`SAV`); `tests/cartridge-save.test.ts` compares its struct offsets (`LAYOUT`) with the pinned build's symbols.
+- Copy selection follows `TryLoadSaveFile`: check values and the 16-bit checksum of the main copy, else the backup's; both damaged, or never saved, is refused. Boxes come from their own banks (`LoadBox` copies the current one into `sBox`), party mail and the mailbox from their backups (`RestorePartyMonMail`), the Battle Tower's received reward becomes a won challenge (`LoadPlayerData`).
+- The clock: with an emulator footer, the MBC3 registers plus the time since the file was written (unless halted), nine-bit days modulo 140 and `wStart*` added with carries; without one, the device's time and the saved `wCurDay`. The minute and weekday offsets reproduce that time and weekday; the Lucky Number countdown, its drawn day and the daily reset move with the difference between `wCurDay` and the port's day number.
+- Names keep the naming screen's alphabet, with <PK> and <MN> as `ᴾᴷ`/`ᴹᴺ` (one character, one tile); player and OT names now accept that alphabet. Boxed Eggs validate (they keep their `egg` mark). Native states up to 256 kB load, enough for a full PC.
+- Refused with the reason: unported maps, the Bug-Catching Contest, a Battle Tower challenge in progress, characters outside the naming screen (traded Japanese names, ligatures). Not carried over, with a note in the preview: the tiles walked count, Mystery Gift items, link battle records; time-windowed objects follow the clock again.
+- Savegames → Import backup reads `.sav`/`.srm`/`.dat` files (or any 32 KiB non-JSON file), previews trainer, place, progress, which copy and clock were used and the notes, then adds or replaces a save like a native backup (`SlotSession.previewCartridge`). Tests: `tests/cartridge-save.test.ts` (the committed real `.sav` and Virtual Console `sav.dat`, backup fallback, clock footers, day counters, refusals), `tests/save-slots.test.ts` and `tests/save-slots-browser.spec.ts`.
+
 ## Native battles: current state
 
 The battle core, ROM tables, encounter hooks, battle UI and whiteout hooks are present. Unit tests cover wins, escape, loss, experience, move learning and capture; reference tests compare damage, type effectiveness, stat calculation and experience curves. Browser tests drive a test-only wild encounter through the real UI: victory with level-up and move learning, escape, whiteout, catching with a nickname, keyboard and on-screen D-pad menu navigation, mid-battle backup restore, rollback of unsupported effects, switching through the party menu and a Potion from the Items pocket. Real Route 29 encounters now use the ROM's encounter tables. Every ball can be thrown; only the contest's Park Ball handling remains.
@@ -643,6 +652,7 @@ Acceptance: main-game/postgame playthroughs, representative optional content, ba
 - [x] Scalable text and configurable keyboard controls
 - [ ] Fuller accessibility: announcements for every native screen and touch control remapping
 - [x] Save slots with migration, atomic writes and import previews
+- [x] Cartridge `.sav` import with verified structure, checksums and clock conversion (board #44)
 - [x] Installable web app with offline app shell, safe updates and quota handling
 - [ ] Acceptance on physical iPhone and Android devices
 
@@ -656,7 +666,7 @@ Dependencies: stable serialization for every system stored in a slot, migration
 
 Acceptance: migrate existing browser data without loss, keep several independent playthroughs, recover from interrupted writes and reject incompatible or corrupt imports without changing a valid slot. Test create/load/delete/rename/duplicate, autosave isolation, export/import conflicts and upgrades from every released schema.
 
-Add PWA installation/offline caching of the app shell only. ROM/data retention remains a separate explicit local preference; otherwise reselect the ROM after reopening. Add safe application updates, schema migrations, storage persistence/quota handling and portable backups. Investigate original `.sav` import only with verified structure, checksums and RTC conversion.
+Add PWA installation/offline caching of the app shell only. ROM/data retention remains a separate explicit local preference; otherwise reselect the ROM after reopening. Add safe application updates, schema migrations, storage persistence/quota handling and portable backups. Original `.sav` files import through a converter with verified structure, checksums and RTC conversion (board #44, below).
 
 Acceptance: installation, offline startup, portrait/landscape, touch/audio, background/resume and updates on physical iPhone/Safari and Android/Chrome. Browser automation does not establish physical-device compatibility.