Keep several saves, with migration, atomic writes and import previews (Closes #37)

Savegames now lists independent save slots made with the loaded ROM:
new game, continue, rename, duplicate, export and delete. The native
database moves to IndexedDB version 2; the singleton save becomes
"Save 1" inside the upgrade transaction, so it migrates exactly once and
the old store is left untouched. Each write adds a generation and drops
older ones in one transaction, keeping two records with CRC-32
checksums: a damaged newest record falls back to the previous one.
Slots and records from a newer player are kept and never written.

Imports are checked in a scratch world before anything changes and
previewed with the trainer, progress, saved time, game data version and
the slots of the same trainer; they go into a new save or replace one,
whose previous record stays recoverable.

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

tests/native.test.ts

@@ -575,6 +575,54 @@ describe.skipIf(!existsSync(romPath))(
       expect(world.save().playerId).toBeLessThan(0x10000);
       expect(() => world.restore({ ...legacy, version: 4 })).toThrow("Invalid");
     });
+    it("describes saves of every schema for the Savegames list", () => {
+      const world = new GameWorld(load(), () => new Date("2026-09-22T12:00:00"));
+      const flags = [27, 28, 29];
+      const town = world.assets.map("24:4");
+      const land = Array.from({ length: town.width * town.height }, (_, i) => ({
+        x: i % town.width,
+        y: Math.floor(i / town.width),
+      })).find(
+        ({ x, y }) =>
+          world.assets.permission(world.assets.collision(town, x, y)) === 0,
+      )!;
+      world.restore({
+        ...world.save(),
+        name: "GOLD",
+        map: "24:4",
+        ...land,
+        flags,
+        gameTime: { hours: 3, minutes: 7, seconds: 0, frames: 0, capped: false },
+        pokedex: { seen: [152, 16], caught: [152] },
+      });
+      const current = world.save();
+      expect(world.describe()).toEqual({
+        player: "GOLD",
+        playerId: current.playerId,
+        place: "NEW BARK TOWN",
+        hours: 3,
+        minutes: 7,
+        badges: 3,
+        caught: 1,
+        newGame: false,
+      });
+      // Indoors, the landmark is the map's own (the player's house).
+      world.restore({ ...current, map: "24:6", x: 6, y: 6 });
+      expect(world.describe().place).toBe("NEW BARK TOWN");
+      const { scenes, phone, clock, objects, playerId, party, bag, pokedex, ...legacy } =
+        current;
+      void [scenes, phone, clock, objects, playerId, party, bag, pokedex];
+      for (const version of [1, 2]) {
+        const scratch = new GameWorld(load(), () => new Date("2026-09-22T12:00:00"));
+        scratch.restore({ ...legacy, version, ...(version === 2 && { scenes: {}, phone: [], clock, objects: [] }) });
+        expect(scratch.describe()).toMatchObject({
+          player: "GOLD",
+          place: "NEW BARK TOWN",
+          badges: 3,
+          caught: 0,
+        });
+      }
+    });
     it("decodes species, moves, items and growth from the ROM", () => {
       const data = load().pokemon;
       expect([152, 155, 158].map((id) => data.speciesName(id))).toEqual([