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/handler/backup_handler.go

@@ -0,0 +1,49 @@
+package handler
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	"dating-app/internal/service"
+	"dating-app/internal/utils"
+)
+
+type BackupHandler struct {
+	backupService *service.BackupService
+}
+
+func NewBackupHandler(backupService *service.BackupService) *BackupHandler {
+	return &BackupHandler{backupService: backupService}
+}
+
+// List GET /admin/backups
+func (h *BackupHandler) List(c *gin.Context) {
+	backups, err := h.backupService.List()
+	if err != nil {
+		utils.Fail(c, http.StatusInternalServerError, "خطا در دریافت لیست بک‌آپ‌ها", nil)
+		return
+	}
+	utils.Success(c, http.StatusOK, "", backups)
+}
+
+// Create POST /admin/backups
+func (h *BackupHandler) Create(c *gin.Context) {
+	info, err := h.backupService.Create()
+	if err != nil {
+		utils.Fail(c, http.StatusInternalServerError, "گرفتن بک‌آپ ناموفق بود: "+err.Error(), nil)
+		return
+	}
+	utils.Success(c, http.StatusCreated, "بک‌آپ با موفقیت ساخته شد", info)
+}
+
+// Download GET /admin/backups/:filename
+func (h *BackupHandler) Download(c *gin.Context) {
+	filename := c.Param("filename")
+	path, err := h.backupService.ResolvePath(filename)
+	if err != nil {
+		utils.Fail(c, http.StatusNotFound, "فایل بک‌آپ یافت نشد", nil)
+		return
+	}
+	c.FileAttachment(path, filename)
+}