Fix 113 hardening issues across entire Go backend

Security:
- Replace all binding: tags with validate: + c.Validate() in admin handlers
- Add rate limiting to auth endpoints (login, register, password reset)
- Add security headers (HSTS, XSS protection, nosniff, frame options)
- Wire Google Pub/Sub token verification into webhook handler
- Replace ParseUnverified with proper OIDC/JWKS key verification
- Verify inner Apple JWS signatures in webhook handler
- Add io.LimitReader (1MB) to all webhook body reads
- Add ownership verification to file deletion
- Move hardcoded admin credentials to env vars
- Add uniqueIndex to User.Email
- Hide ConfirmationCode from JSON serialization
- Mask confirmation codes in admin responses
- Use http.DetectContentType for upload validation
- Fix path traversal in storage service
- Replace os.Getenv with Viper in stripe service
- Sanitize Redis URLs before logging
- Separate DEBUG_FIXED_CODES from DEBUG flag
- Reject weak SECRET_KEY in production
- Add host check on /_next/* proxy routes
- Use explicit localhost CORS origins in debug mode
- Replace err.Error() with generic messages in all admin error responses

Critical fixes:
- Rewrite FCM to HTTP v1 API with OAuth 2.0 service account auth
- Fix user_customuser -> auth_user table names in raw SQL
- Fix dashboard verified query to use UserProfile model
- Add escapeLikeWildcards() to prevent SQL wildcard injection

Bug fixes:
- Add bounds checks for days/expiring_soon query params (1-3650)
- Add receipt_data/transaction_id empty-check to RestoreSubscription
- Change Active bool -> *bool in device handler
- Check all unchecked GORM/FindByIDWithProfile errors
- Add validation for notification hour fields (0-23)
- Add max=10000 validation on task description updates

Transactions & data integrity:
- Wrap registration flow in transaction
- Wrap QuickComplete in transaction
- Move image creation inside completion transaction
- Wrap SetSpecialties in transaction
- Wrap GetOrCreateToken in transaction
- Wrap completion+image deletion in transaction

Performance:
- Batch completion summaries (2 queries vs 2N)
- Reuse single http.Client in IAP validation
- Cache dashboard counts (30s TTL)
- Batch COUNT queries in admin user list
- Add Limit(500) to document queries
- Add reminder_stage+due_date filters to reminder queries
- Parse AllowedTypes once at init
- In-memory user cache in auth middleware (30s TTL)
- Timezone change detection cache
- Optimize P95 with per-endpoint sorted buffers
- Replace crypto/md5 with hash/fnv for ETags

Code quality:
- Add sync.Once to all monitoring Stop()/Close() methods
- Replace 8 fmt.Printf with zerolog in auth service
- Log previously discarded errors
- Standardize delete response shapes
- Route hardcoded English through i18n
- Remove FileURL from DocumentResponse (keep MediaURL only)
- Thread user timezone through kanban board responses
- Initialize empty slices to prevent null JSON
- Extract shared field map for task Update/UpdateTx
- Delete unused SoftDeleteModel, min(), formatCron, legacy handlers

Worker & jobs:
- Wire Asynq email infrastructure into worker
- Register HandleReminderLogCleanup with daily 3AM cron
- Use per-user timezone in HandleSmartReminder
- Replace direct DB queries with repository calls
- Delete legacy reminder handlers (~200 lines)
- Delete unused task type constants

Dependencies:
- Replace archived jung-kurt/gofpdf with go-pdf/fpdf
- Replace unmaintained gomail.v2 with wneessen/go-mail
- Add TODO for Echo jwt v3 transitive dep removal

Test infrastructure:
- Fix MakeRequest/SeedLookupData error handling
- Replace os.Exit(0) with t.Skip() in scope/consistency tests
- Add 11 new FCM v1 tests

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/handlers/upload_handler.go

@@ -7,19 +7,31 @@ import (
 	"github.com/rs/zerolog/log"
 
 	"github.com/treytartt/honeydue-api/internal/apperrors"
+	"github.com/treytartt/honeydue-api/internal/dto/responses"
+	"github.com/treytartt/honeydue-api/internal/i18n"
 	"github.com/treytartt/honeydue-api/internal/middleware"
-	"github.com/treytartt/honeydue-api/internal/models"
 	"github.com/treytartt/honeydue-api/internal/services"
 )
 
+// FileOwnershipChecker verifies whether a user owns a file referenced by URL.
+// Implementations should check associated records (e.g., task completion images,
+// document files, document images) to determine ownership.
+type FileOwnershipChecker interface {
+	IsFileOwnedByUser(fileURL string, userID uint) (bool, error)
+}
+
 // UploadHandler handles file upload endpoints
 type UploadHandler struct {
-	storageService *services.StorageService
+	storageService      *services.StorageService
+	fileOwnershipChecker FileOwnershipChecker
 }
 
 // NewUploadHandler creates a new upload handler
-func NewUploadHandler(storageService *services.StorageService) *UploadHandler {
-	return &UploadHandler{storageService: storageService}
+func NewUploadHandler(storageService *services.StorageService, fileOwnershipChecker FileOwnershipChecker) *UploadHandler {
+	return &UploadHandler{
+		storageService:      storageService,
+		fileOwnershipChecker: fileOwnershipChecker,
+	}
 }
 
 // UploadImage handles POST /api/uploads/image
@@ -83,13 +95,14 @@ type DeleteFileRequest struct {
 
 // DeleteFile handles DELETE /api/uploads
 // Expects JSON body with "url" field.
-//
-// TODO(SEC-18): Add ownership verification. Currently any authenticated user can delete
-// any file if they know the URL. The upload system does not track which user uploaded
-// which file, so a proper fix requires adding an uploads table or file ownership metadata.
-// For now, deletions are logged with user ID for audit trail, and StorageService.Delete
-// enforces path containment to prevent deleting files outside the upload directory.
+// Verifies that the requesting user owns the file by checking associated records
+// (task completion images, document files/images) before allowing deletion.
 func (h *UploadHandler) DeleteFile(c echo.Context) error {
+	user, err := middleware.MustGetAuthUser(c)
+	if err != nil {
+		return err
+	}
+
 	var req DeleteFileRequest
 
 	if err := c.Bind(&req); err != nil {
@@ -100,17 +113,28 @@ func (h *UploadHandler) DeleteFile(c echo.Context) error {
 		return apperrors.BadRequest("error.url_required")
 	}
 
-	// Log the deletion with user ID for audit trail
-	if user, ok := c.Get(middleware.AuthUserKey).(*models.User); ok {
-		log.Info().
-			Uint("user_id", user.ID).
-			Str("file_url", req.URL).
-			Msg("File deletion requested")
+	// Verify ownership: the user must own a record that references this file URL
+	if h.fileOwnershipChecker != nil {
+		owned, err := h.fileOwnershipChecker.IsFileOwnedByUser(req.URL, user.ID)
+		if err != nil {
+			log.Error().Err(err).Uint("user_id", user.ID).Str("file_url", req.URL).Msg("Failed to check file ownership")
+			return apperrors.Internal(err)
+		}
+		if !owned {
+			log.Warn().Uint("user_id", user.ID).Str("file_url", req.URL).Msg("Unauthorized file deletion attempt")
+			return apperrors.Forbidden("error.file_access_denied")
+		}
 	}
 
+	// Log the deletion with user ID for audit trail
+	log.Info().
+		Uint("user_id", user.ID).
+		Str("file_url", req.URL).
+		Msg("File deletion requested")
+
 	if err := h.storageService.Delete(req.URL); err != nil {
 		return err
 	}
 
-	return c.JSON(http.StatusOK, map[string]interface{}{"message": "File deleted successfully"})
+	return c.JSON(http.StatusOK, responses.MessageResponse{Message: i18n.LocalizedMessage(c, "message.file_deleted")})
 }