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>

vitest.config.ts

@@ -18,8 +18,8 @@ export default defineConfig({
 					branches: 90,
 				},
 				"apps/web/src/adapters": {
-					lines: 68,
-					branches: 56,
+					lines: 80,
+					branches: 62,
 				},
 				"apps/web/src/persistence": {
 					lines: 85,