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-combatant.ts

@@ -0,0 +1,12 @@
+import type { Combatant } from "@initiative/domain";
+import { combatantId } from "@initiative/domain";
+
+let counter = 0;
+
+export function buildCombatant(overrides?: Partial<Combatant>): Combatant {
+	return {
+		id: combatantId(`c-${++counter}`),
+		name: "Combatant",
+		...overrides,
+	};
+}