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/features/combat/EncounterTracker.tsx

@@ -36,7 +36,8 @@ export function EncounterTracker({ encounter, campaign }: { encounter: Encounter
   const mutate = (fn: (e: Encounter) => Encounter) => {
     undoStack.current.push(encounter);
     if (undoStack.current.length > 50) undoStack.current.shift();
-    void encountersRepo.save(fn(encounter));
+    // Transactional read-modify-write so rapid mutations can't clobber each other.
+    void encountersRepo.mutate(encounter.id, fn);
   };
   const undo = () => {
     const prev = undoStack.current.pop();