Phase 8: player view (local/projector) + sync seam

- Player View (/play): read-only projector screen — party HP bars + conditions,
  active-encounter initiative with current turn; enemy HP hidden behind a
  Healthy/Bloodied/Down status band; Fullscreen button
- SyncAdapter seam (src/lib/sync): local-first default via Dexie liveQuery;
  documents where a future networked (WebSocket/CRDT) backend plugs in
- Dashboard + routes get a Player View entry
- Robustness: encountersRepo.mutate() does transactional read-modify-write so
  rapid combat mutations can't overwrite each other (old C19 race); tracker uses it

New player-view e2e. Networked multiplayer backend intentionally deferred.

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

src/lib/db/repositories.ts

@@ -164,6 +164,19 @@ export const encountersRepo = {
     await db.encounters.put(validated);
   },
 
+  /**
+   * Apply a transition by reading the freshest committed state inside a
+   * transaction, so two rapid mutations can't overwrite each other (the
+   * read-modify-write race the old app shipped — bug class C19).
+   */
+  async mutate(id: string, fn: (e: Encounter) => Encounter): Promise<void> {
+    await db.transaction('rw', db.encounters, async () => {
+      const current = await db.encounters.get(id);
+      if (!current) return;
+      await db.encounters.put(encounterSchema.parse({ ...fn(current), updatedAt: now() }));
+    });
+  },
+
   async remove(id: string): Promise<void> {
     await db.encounters.delete(id);
   },