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/document_handler.go

@@ -12,6 +12,8 @@ import (
 
 	"github.com/treytartt/honeydue-api/internal/apperrors"
 	"github.com/treytartt/honeydue-api/internal/dto/requests"
+	"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/repositories"
@@ -60,6 +62,9 @@ func (h *DocumentHandler) ListDocuments(c echo.Context) error {
 		}
 		if es := c.QueryParam("expiring_soon"); es != "" {
 			if parsed, err := strconv.Atoi(es); err == nil {
+				if parsed < 1 || parsed > 3650 {
+					return apperrors.BadRequest("error.days_out_of_range")
+				}
 				filter.ExpiringSoon = &parsed
 			}
 		}
@@ -192,7 +197,10 @@ func (h *DocumentHandler) CreateDocument(c echo.Context) error {
 			}
 		}
 
-		if uploadedFile != nil && h.storageService != nil {
+		if uploadedFile != nil {
+			if h.storageService == nil {
+				return apperrors.Internal(nil)
+			}
 			result, err := h.storageService.Upload(uploadedFile, "documents")
 			if err != nil {
 				return apperrors.BadRequest("error.failed_to_upload_file")
@@ -262,7 +270,7 @@ func (h *DocumentHandler) DeleteDocument(c echo.Context) error {
 	if err != nil {
 		return err
 	}
-	return c.JSON(http.StatusOK, map[string]interface{}{"message": "Document deleted successfully"})
+	return c.JSON(http.StatusOK, responses.MessageResponse{Message: i18n.LocalizedMessage(c, "message.document_deleted")})
 }
 
 // ActivateDocument handles POST /api/documents/:id/activate/
@@ -280,7 +288,7 @@ func (h *DocumentHandler) ActivateDocument(c echo.Context) error {
 	if err != nil {
 		return err
 	}
-	return c.JSON(http.StatusOK, map[string]interface{}{"message": "Document activated successfully", "document": response})
+	return c.JSON(http.StatusOK, response)
 }
 
 // DeactivateDocument handles POST /api/documents/:id/deactivate/
@@ -298,7 +306,7 @@ func (h *DocumentHandler) DeactivateDocument(c echo.Context) error {
 	if err != nil {
 		return err
 	}
-	return c.JSON(http.StatusOK, map[string]interface{}{"message": "Document deactivated successfully", "document": response})
+	return c.JSON(http.StatusOK, response)
 }
 
 // UploadDocumentImage handles POST /api/documents/:id/images/