V2 P5-backend + P7 + P8: conflict-safe sync, revocable invites, feats, multiclass, tests

P5 backend (the deferred items):
- conflict-aware cloud sync via optimistic concurrency: the server versions each
  backup blob (file mtime) and rejects a push whose base version is stale (409),
  so a second device can't silently overwrite a newer cloud copy. The client
  tracks its last-synced version; the SyncStatusIndicator surfaces a "Sync
  conflict" with one-click resolution (Use cloud / Keep this device), and the
  Settings push offers the same choice.
- revocable invites: owner can rotate a campaign's invite code (kills the old
  one) and remove a member (drops them + deletes their published characters).
  (Skipped editor/player roles — no enforcement target in the current model.)
- image storage: deliberately deferred (live images already stream de-duped on a
  separate channel; a backup blob-store is infra with no correctness gain).

P7 — subclass/feat/multiclass depth:
- feats are now first-class tracked records (name + effect text) in a Feats &
  Features sheet section, not buried in notes. Dexie v15 migration.
- 5e multiclass spell-slot calculator: a pure multiclassSlots() (full ×1, half
  ÷2, third ÷3 → full-caster table) + a sheet control to fill the slot table for
  multiclass casters. (Honest scope: tracking + slots, not per-subclass feature
  automation.)

P8 — test hardening: v2-surfaces e2e (feats, multiclass calc, signals bell,
World nav) + server tests (blob versioning, invite rotation, member removal) +
multiclass unit tests.

Gate green: 283 unit + 35 e2e + 2 realtime. App + server build clean.

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

src/features/characters/CharacterSheet.tsx

@@ -24,6 +24,7 @@ import { AttacksSection } from './sheet/AttacksSection';
 import { ResourcesSection } from './sheet/ResourcesSection';
 import { SpellcastingSection } from './sheet/SpellcastingSection';
 import { DefensesSection } from './sheet/DefensesSection';
+import { FeatsSection } from './sheet/FeatsSection';
 import { AbilityGenModal } from './sheet/AbilityGenModal';
 import { LevelUpModal } from './sheet/LevelUpModal';
 
@@ -288,6 +289,9 @@ export function CharacterSheet({ character }: { character: Character }) {
       {/* Class resources + rest */}
       <ResourcesSection c={c} update={update} />
 
+      {/* Feats & features */}
+      <FeatsSection c={c} update={update} />
+
       {/* Inventory, currency, encumbrance */}
       <InventorySection c={c} update={update} />