Add production hardening: monitoring, backups, caching, and high-traffic resilience

- Recovery middleware (no more crash-on-panic), request metrics/monitoring
  store + admin API, in-memory TTL caching for read-heavy option/question/
  category lookups, gzip + rate-limiting middleware, sanitized chat message
  encoding, and pg_dump-based database backups with an admin API.
- Fix N+1 queries in the discover feed, candidate detail, and match list
  endpoints by batching selection/photo/user/last-message lookups into
  single queries instead of one-per-item loops.
- Tune DB connection pooling and add HTTP server timeouts + graceful
  shutdown so the API degrades gracefully instead of falling over under load.
- Fix a null (vs empty array) JSON response for candidates/matches without
  photos or interests, which crashed the web app's swipe card.

internal/repository/question_repository.go

@@ -1,23 +1,40 @@
 package repository
 
 import (
+	"time"
+
 	"gorm.io/gorm"
 
+	"dating-app/internal/cache"
 	"dating-app/internal/models"
 )
 
+const activeQuestionsCacheTTL = 5 * time.Minute
+const activeQuestionsCacheKey = "active"
+
 type QuestionRepository struct {
-	db *gorm.DB
+	db          *gorm.DB
+	activeCache *cache.TTLCache[string, []models.ProfileQuestion]
 }
 
 func NewQuestionRepository(db *gorm.DB) *QuestionRepository {
-	return &QuestionRepository{db: db}
+	return &QuestionRepository{
+		db:          db,
+		activeCache: cache.New[string, []models.ProfileQuestion](activeQuestionsCacheTTL),
+	}
 }
 
 func (r *QuestionRepository) ListActive() ([]models.ProfileQuestion, error) {
+	if cached, ok := r.activeCache.Get(activeQuestionsCacheKey); ok {
+		return cached, nil
+	}
 	var qs []models.ProfileQuestion
 	err := r.db.Where("is_active = ?", true).Order("sort_order asc, id asc").Find(&qs).Error
-	return qs, err
+	if err != nil {
+		return nil, err
+	}
+	r.activeCache.Set(activeQuestionsCacheKey, qs)
+	return qs, nil
 }
 
 func (r *QuestionRepository) ListAllAdmin() ([]models.ProfileQuestion, error) {
@@ -42,15 +59,27 @@ func (r *QuestionRepository) FindActiveByIDs(ids []uint) ([]models.ProfileQuesti
 }
 
 func (r *QuestionRepository) Create(q *models.ProfileQuestion) error {
-	return r.db.Create(q).Error
+	if err := r.db.Create(q).Error; err != nil {
+		return err
+	}
+	r.activeCache.Clear()
+	return nil
 }
 
 func (r *QuestionRepository) Update(q *models.ProfileQuestion) error {
-	return r.db.Save(q).Error
+	if err := r.db.Save(q).Error; err != nil {
+		return err
+	}
+	r.activeCache.Clear()
+	return nil
 }
 
 func (r *QuestionRepository) Delete(id uint) error {
-	return r.db.Delete(&models.ProfileQuestion{}, id).Error
+	if err := r.db.Delete(&models.ProfileQuestion{}, id).Error; err != nil {
+		return err
+	}
+	r.activeCache.Clear()
+	return nil
 }
 
 // ReplaceUserAnswers پاسخ‌های قبلی کاربر رو با پاسخ‌های جدید جایگزین می‌کنه (تراکنشی)