refactor(db): collapse repository rollout scaffolding into single factory

Repositories are now the only data path. Replaces the 41 current-*-repository
wrapper files, the DATABASE_LAYER_REPOSITORY_ROLLOUT flag/alias map and the
unused database/runtime adapter with repositories/factory.ts, a plain
DatabaseContext type and an in-memory TestSqliteDatabase test harness.

src/backend/utils/credential-system-encryption-migration.test.ts

@@ -13,19 +13,13 @@ const sharedCredentialRepository = {
   markNeedsReEncryptionByOriginalCredentialId: vi.fn(),
 };
 
-vi.mock("../database/repositories/current-credential-repository.js", () => ({
+vi.mock("../database/repositories/factory.js", () => ({
   createCurrentCredentialRepository: vi.fn(() => credentialRepository),
+  createCurrentSharedCredentialRepository: vi.fn(
+    () => sharedCredentialRepository,
+  ),
 }));
 
-vi.mock(
-  "../database/repositories/current-shared-credential-repository.js",
-  () => ({
-    createCurrentSharedCredentialRepository: vi.fn(
-      () => sharedCredentialRepository,
-    ),
-  }),
-);
-
 describe("CredentialSystemEncryptionMigration", () => {
   beforeEach(() => {
     vi.restoreAllMocks();