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/admin/handlers/completion_image_handler.go

@@ -35,8 +35,8 @@ type AdminCompletionImageResponse struct {
 
 // CreateCompletionImageRequest represents the request to create a completion image
 type CreateCompletionImageRequest struct {
-	CompletionID uint   `json:"completion_id" binding:"required"`
-	ImageURL     string `json:"image_url" binding:"required"`
+	CompletionID uint   `json:"completion_id" validate:"required"`
+	ImageURL     string `json:"image_url" validate:"required"`
 	Caption      string `json:"caption"`
 }
 
@@ -50,7 +50,7 @@ type UpdateCompletionImageRequest struct {
 func (h *AdminCompletionImageHandler) List(c echo.Context) error {
 	var filters dto.PaginationParams
 	if err := c.Bind(&filters); err != nil {
-		return c.JSON(http.StatusBadRequest, map[string]interface{}{"error": err.Error()})
+		return c.JSON(http.StatusBadRequest, map[string]interface{}{"error": "Invalid request body"})
 	}
 
 	// Optional completion_id filter
@@ -91,10 +91,39 @@ func (h *AdminCompletionImageHandler) List(c echo.Context) error {
 		return c.JSON(http.StatusInternalServerError, map[string]interface{}{"error": "Failed to fetch completion images"})
 	}
 
+	// Batch-load completion+task info to avoid N+1 queries
+	completionIDs := make([]uint, 0, len(images))
+	for _, img := range images {
+		completionIDs = append(completionIDs, img.CompletionID)
+	}
+
+	completionMap := make(map[uint]models.TaskCompletion)
+	if len(completionIDs) > 0 {
+		var completions []models.TaskCompletion
+		h.db.Preload("Task").Where("id IN ?", completionIDs).Find(&completions)
+		for _, c := range completions {
+			completionMap[c.ID] = c
+		}
+	}
+
 	// Build response with task info
 	responses := make([]AdminCompletionImageResponse, len(images))
 	for i, image := range images {
-		responses[i] = h.toResponse(&image)
+		response := AdminCompletionImageResponse{
+			ID:           image.ID,
+			CompletionID: image.CompletionID,
+			ImageURL:     image.ImageURL,
+			Caption:      image.Caption,
+			CreatedAt:    image.CreatedAt.Format("2006-01-02T15:04:05Z"),
+			UpdatedAt:    image.UpdatedAt.Format("2006-01-02T15:04:05Z"),
+		}
+		if comp, ok := completionMap[image.CompletionID]; ok {
+			response.TaskID = comp.TaskID
+			if comp.Task.ID != 0 {
+				response.TaskTitle = comp.Task.Title
+			}
+		}
+		responses[i] = response
 	}
 
 	return c.JSON(http.StatusOK, dto.NewPaginatedResponse(responses, total, filters.GetPage(), filters.GetPerPage()))
@@ -122,7 +151,10 @@ func (h *AdminCompletionImageHandler) Get(c echo.Context) error {
 func (h *AdminCompletionImageHandler) Create(c echo.Context) error {
 	var req CreateCompletionImageRequest
 	if err := c.Bind(&req); err != nil {
-		return c.JSON(http.StatusBadRequest, map[string]interface{}{"error": err.Error()})
+		return c.JSON(http.StatusBadRequest, map[string]interface{}{"error": "Invalid request body"})
+	}
+	if err := c.Validate(&req); err != nil {
+		return err
 	}
 
 	// Verify completion exists
@@ -164,7 +196,7 @@ func (h *AdminCompletionImageHandler) Update(c echo.Context) error {
 
 	var req UpdateCompletionImageRequest
 	if err := c.Bind(&req); err != nil {
-		return c.JSON(http.StatusBadRequest, map[string]interface{}{"error": err.Error()})
+		return c.JSON(http.StatusBadRequest, map[string]interface{}{"error": "Invalid request body"})
 	}
 
 	if req.ImageURL != nil {
@@ -207,14 +239,15 @@ func (h *AdminCompletionImageHandler) Delete(c echo.Context) error {
 func (h *AdminCompletionImageHandler) BulkDelete(c echo.Context) error {
 	var req dto.BulkDeleteRequest
 	if err := c.Bind(&req); err != nil {
-		return c.JSON(http.StatusBadRequest, map[string]interface{}{"error": err.Error()})
+		return c.JSON(http.StatusBadRequest, map[string]interface{}{"error": "Invalid request body"})
 	}
 
-	if err := h.db.Where("id IN ?", req.IDs).Delete(&models.TaskCompletionImage{}).Error; err != nil {
+	result := h.db.Where("id IN ?", req.IDs).Delete(&models.TaskCompletionImage{})
+	if result.Error != nil {
 		return c.JSON(http.StatusInternalServerError, map[string]interface{}{"error": "Failed to delete completion images"})
 	}
 
-	return c.JSON(http.StatusOK, map[string]interface{}{"message": "Completion images deleted successfully", "count": len(req.IDs)})
+	return c.JSON(http.StatusOK, map[string]interface{}{"message": "Completion images deleted successfully", "count": result.RowsAffected})
 }
 
 // toResponse converts a TaskCompletionImage model to AdminCompletionImageResponse