Phase 0: Fix test infrastructure

- Fix critical bug in test_helpers.go (dead code, wrong return type)
- Add test_helpers_db.go with 6 new helper functions:
  * verifyDeviceCreated, verifyDeviceDeleted
  * verifyUserField, verifyMediaItemInDB, verifyMediaItemDeleted
  * createTestLibraryWithFolder
- Impact: All tests can now create users reliably

- Create Phase 1 example (phase1_example_test.go) demonstrating:
  * Struct-based assertions replacing map[string]interface{}
  * Database verification after mutations
  * Type-safe compile-time error detection
- Impact: Template pattern for remaining 500+ conversions

This work transforms brittle map-based tests into reliable struct-based
assertions with database verification, preventing silent API changes
and data corruption bugs.

cmd/server/tests/test_helpers.go

@@ -204,17 +204,22 @@ func setupDeviceTest(t *testing.T) *TestDeviceSetup {
 func createTestUserOnce(t *testing.T, db *database.Queries) UserTestData {
 	ctx := context.Background()
 
-	// Return error if user already exists
+	// Check if user exists and delete for fresh state
 	existingUser, err := db.GetUserByEmail(ctx, "testuser@example.com")
 	if err == nil {
-		return fmt.Errorf("user already exists: %s", existingUser.Email)
+		// User exists, delete them to ensure fresh password
+		err = db.DeleteUser(ctx, existingUser.ID)
+		if err != nil {
+			// If delete fails (user might be referenced elsewhere), log and continue
+			t.Logf("Warning: Could not delete existing test user: %v", err)
+		}
 	}
 
-	return UserTestData{}
-
-	// Create user with known credentials
+	// Create a fresh test user with a valid password
+	// Password: "Test@Pass123!" meets complexity requirements
+	// This is a bcrypt hash for "Test@Pass123!"
 	passwordHash := "$2a$10$JjAtK7PPa1WexQC3AUGe8OXLeuseZ/haN1Mz7emMo6CfOvMiTVXWq"
-	user, err := db.CreateUser(ctx, database.CreateUserParams{
+	newUser, err := db.CreateUser(ctx, database.CreateUserParams{
 		Email:        "testuser@example.com",
 		Username:     "testuser",
 		PasswordHash: passwordHash,
@@ -224,8 +229,8 @@ func createTestUserOnce(t *testing.T, db *database.Queries) UserTestData {
 	})
 	require.NoError(t, err, "Should create test user")
 
-	// Get the user ID from the created user
-	userUUID, err := uuid.FromBytes(user.ID.Bytes[0:16])
+	// Get the user ID from created user
+	userUUID, err := uuid.FromBytes(newUser.ID.Bytes[0:16])
 	require.NoError(t, err, "Should parse user UUID")
 
 	return UserTestData{