Introduce adapter injection and migrate test suite

Replace direct adapter/persistence imports with context-based injection
(AdapterContext + useAdapters) so tests use in-memory implementations
instead of vi.mock. Migrate component tests from context mocking to
AllProviders with real hooks. Extract export/import logic from ActionBar
into useEncounterExportImport hook. Add bestiary-cache and
bestiary-index-adapter test suites. Raise adapter coverage thresholds
(68→80 lines, 56→62 branches).

77 test files, 891 tests, all passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/src/__tests__/factories/build-encounter.ts

@@ -0,0 +1,10 @@
+import type { Encounter } from "@initiative/domain";
+
+export function buildEncounter(overrides?: Partial<Encounter>): Encounter {
+	return {
+		combatants: [],
+		activeIndex: 0,
+		roundNumber: 1,
+		...overrides,
+	};
+}