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/middleware/auth.go

@@ -25,19 +25,24 @@ const (
 	TokenCacheTTL = 5 * time.Minute
 	// TokenCachePrefix is the prefix for token cache keys
 	TokenCachePrefix = "auth_token_"
+	// UserCacheTTL is how long full user records are cached in memory to
+	// avoid hitting the database on every authenticated request.
+	UserCacheTTL = 30 * time.Second
 )
 
 // AuthMiddleware provides token authentication middleware
 type AuthMiddleware struct {
-	db    *gorm.DB
-	cache *services.CacheService
+	db        *gorm.DB
+	cache     *services.CacheService
+	userCache *UserCache
 }
 
 // NewAuthMiddleware creates a new auth middleware instance
 func NewAuthMiddleware(db *gorm.DB, cache *services.CacheService) *AuthMiddleware {
 	return &AuthMiddleware{
-		db:    db,
-		cache: cache,
+		db:        db,
+		cache:     cache,
+		userCache: NewUserCache(UserCacheTTL),
 	}
 }
 
@@ -138,7 +143,8 @@ func extractToken(c echo.Context) (string, error) {
 	return token, nil
 }
 
-// getUserFromCache tries to get user from Redis cache
+// getUserFromCache tries to get user from Redis cache, then from the
+// in-memory user cache, before falling back to the database.
 func (m *AuthMiddleware) getUserFromCache(ctx context.Context, token string) (*models.User, error) {
 	if m.cache == nil {
 		return nil, fmt.Errorf("cache not available")
@@ -152,10 +158,20 @@ func (m *AuthMiddleware) getUserFromCache(ctx context.Context, token string) (*m
 		return nil, err
 	}
 
-	// Get user from database by ID
+	// Try in-memory user cache first to avoid a DB round-trip
+	if cached := m.userCache.Get(userID); cached != nil {
+		if !cached.IsActive {
+			m.cache.InvalidateAuthToken(ctx, token)
+			m.userCache.Invalidate(userID)
+			return nil, fmt.Errorf("user is inactive")
+		}
+		return cached, nil
+	}
+
+	// In-memory cache miss — fetch from database
 	var user models.User
 	if err := m.db.First(&user, userID).Error; err != nil {
-		// User was deleted - invalidate cache
+		// User was deleted - invalidate caches
 		m.cache.InvalidateAuthToken(ctx, token)
 		return nil, err
 	}
@@ -166,10 +182,13 @@ func (m *AuthMiddleware) getUserFromCache(ctx context.Context, token string) (*m
 		return nil, fmt.Errorf("user is inactive")
 	}
 
+	// Store in in-memory cache for subsequent requests
+	m.userCache.Set(&user)
 	return &user, nil
 }
 
-// getUserFromDatabase looks up the token in the database
+// getUserFromDatabase looks up the token in the database and caches the
+// resulting user record in memory.
 func (m *AuthMiddleware) getUserFromDatabase(token string) (*models.User, error) {
 	var authToken models.AuthToken
 	if err := m.db.Preload("User").Where("key = ?", token).First(&authToken).Error; err != nil {
@@ -181,6 +200,8 @@ func (m *AuthMiddleware) getUserFromDatabase(token string) (*models.User, error)
 		return nil, fmt.Errorf("user is inactive")
 	}
 
+	// Store in in-memory cache for subsequent requests
+	m.userCache.Set(&authToken.User)
 	return &authToken.User, nil
 }
 
@@ -220,7 +241,11 @@ func GetAuthToken(c echo.Context) string {
 	if token == nil {
 		return ""
 	}
-	return token.(string)
+	tokenStr, ok := token.(string)
+	if !ok {
+		return ""
+	}
+	return tokenStr
 }
 
 // MustGetAuthUser retrieves the authenticated user or returns error with 401