Coverage priorities 1-5: test pure functions, extract interfaces, mock-based handler tests

- Priority 1: Test NewSendEmailTask + NewSendPushTask (5 tests)
- Priority 2: Test customHTTPErrorHandler — all 15+ branches (21 tests)
- Priority 3: Extract Enqueuer interface + payload builders in worker pkg (5 tests)
- Priority 4: Extract ClassifyFile/ComputeRelPath in migrate-encrypt (6 tests)
- Priority 5: Define Handler interfaces, refactor to accept them, mock-based tests (14 tests)
- Fix .gitignore: /worker instead of worker to stop ignoring internal/worker/

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/services/auth_refresh_test.go

@@ -35,7 +35,7 @@ func createRefreshTestUser(t *testing.T, db *gorm.DB) *models.User {
 		Email:    "refresh@test.com",
 		IsActive: true,
 	}
-	require.NoError(t, user.SetPassword("password123"))
+	require.NoError(t, user.SetPassword("Password123"))
 	require.NoError(t, db.Create(user).Error)
 	return user
 }