Build MVP: campaigns, characters, combat, dice, compendium

- Rules abstraction (5e + pf2e) behind one interface, fully tested
- Pure combat engine: turn-order safe across add/remove/reorder/init-change
- Dexie storage with real cascade deletes + Zod validation on write
- Seedable dice engine with notation parser
- Lazy SRD compendium (code-split), bestiary -> combat
- Strict TS, 54 unit tests, Playwright e2e smoke (all green)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/db/db.ts

@@ -0,0 +1,32 @@
+import Dexie, { type EntityTable } from 'dexie';
+import type { Campaign } from '@/lib/schemas/campaign';
+import type { Character } from '@/lib/schemas/character';
+import type { Encounter } from '@/lib/schemas/encounter';
+import type { DiceRoll } from '@/lib/schemas/dice';
+
+/**
+ * Single Dexie instance for the whole app. Dexie wraps IndexedDB transactions
+ * correctly (commits before resolving), which removes the silent-data-loss
+ * class of bugs the old hand-rolled adapter shipped with.
+ *
+ * Schema versions are additive: bump `version(n)` and add a `.upgrade()` when
+ * the shape changes — never edit a past version in place.
+ */
+export class TtrpgDatabase extends Dexie {
+  campaigns!: EntityTable<Campaign, 'id'>;
+  characters!: EntityTable<Character, 'id'>;
+  encounters!: EntityTable<Encounter, 'id'>;
+  diceRolls!: EntityTable<DiceRoll, 'id'>;
+
+  constructor() {
+    super('ttrpg-manager');
+    this.version(1).stores({
+      campaigns: 'id, updatedAt',
+      characters: 'id, campaignId, kind',
+      encounters: 'id, campaignId, status',
+      diceRolls: 'id, campaignId, createdAt',
+    });
+  }
+}
+
+export const db = new TtrpgDatabase();