fix: resolve all TypeScript strict-mode errors in test files

- convert-sanitized: use 'as Record' cast for optional mock call args
- error-responses: fix module path (database.js → db.js) and mock return type
- recover-initial-db-fallback: fix mock return type (undefined → true)
- render-timing: remove non-existent .prepare property check
- usage-flush: cast mock request objects to any for test setup

Zero tsc --noEmit errors. 608 tests passing.

src/__tests__/error-responses.test.ts

@@ -226,12 +226,12 @@ describe("Error Response Security - Admin Cleanup", () => {
     const mockAdminAuth = (req: any, res: any, next: any) => next();
 
     // Mock database functions
-    vi.mock("../services/database.js", () => ({
+    vi.mock("../services/db.js", () => ({
       cleanupStaleData: vi.fn(),
     }));
 
-    const { cleanupStaleData } = await import("../services/database.js");
-    vi.mocked(cleanupStaleData).mockResolvedValue({ deletedCount: 5 });
+    const { cleanupStaleData } = await import("../services/db.js");
+    vi.mocked(cleanupStaleData).mockResolvedValue({ expiredVerifications: 3, orphanedUsage: 2 });
 
     // Create minimal app
     app = express();
@@ -250,7 +250,7 @@ describe("Error Response Security - Admin Cleanup", () => {
   });
 
   it("does not expose error message (no 'message' field)", async () => {
-    const { cleanupStaleData } = await import("../services/database.js");
+    const { cleanupStaleData } = await import("../services/db.js");
     const internalError = new Error("Database connection pool exhausted");
     vi.mocked(cleanupStaleData).mockRejectedValue(internalError);