fix: ensure test libraries are cleaned up after each test completes

Problem:
When running `make test-integration`, the last test to run would leave its
"test" libraries in the database. This happened because:

1. setupTestServer() cleaned up old "test" libraries at the START
2. Tests created their own libraries
3. When tests finished, t.Cleanup() called setup.Close() which only closed
   connections but did NOT delete libraries
4. The LAST test's libraries persisted because no subsequent test cleaned them

For example, "Job Status Test Library" from TestWorker_JobStatusTracking
would remain in the database after all tests completed, visible when logging
into the UI.

Root Cause:
The cleanup logic only ran at the START of each test (in setupTestServer),
not at the END. This worked for intermediate tests (each test cleaned up
the previous test's libraries), but the final test had no cleanup.

Solution:
Added library cleanup to the t.Cleanup() function in setupTestServer(). Now
each test deletes its own "test" libraries when it completes, ensuring:
- Clean state after `make test-integration` finishes
- No residual test data in the database
- Safe for tests with subtests (cleanup runs after all subtests finish)

Note on Test Structure:
Tests like TestOPDSEndpoints and TestCollectionSearchLibraryFilter create
libraries once and share them across all subtests. The t.Cleanup() function
runs AFTER all subtests complete, so this change is safe and doesn't
interfere with subtest resource sharing.

Files changed:
- cmd/server/tests/test_helpers_test.go: Added library cleanup to t.Cleanup()

cmd/server/tests/test_helpers_test.go

@@ -616,6 +616,17 @@ func setupTestServer(t *testing.T) *TestServerSetup {
 
 	// Register cleanup function to run automatically when test completes
 	t.Cleanup(func() {
+		// Clean up test libraries created by this test
+		ctx := context.Background()
+		allLibs, err := queries.ListLibraries(ctx)
+		if err == nil {
+			for _, lib := range allLibs {
+				if strings.Contains(strings.ToLower(lib.Name), "test") {
+					queries.DeleteLibrary(ctx, lib.ID)
+				}
+			}
+		}
+
 		if err := setup.Close(); err != nil {
 			t.Errorf("Failed to cleanup test server: %v", err)
 		}