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)
+}

internal/handler/chat_handler.go

@@ -81,6 +81,10 @@ func (h *ChatHandler) handleError(c *gin.Context, err error) {
 	switch {
 	case errors.Is(err, service.ErrNotMatchMember):
 		utils.Fail(c, http.StatusForbidden, err.Error(), nil)
+	case errors.Is(err, utils.ErrInvalidMessageEncoding),
+		errors.Is(err, utils.ErrMessageEmpty),
+		errors.Is(err, utils.ErrMessageTooLong):
+		utils.Fail(c, http.StatusBadRequest, err.Error(), nil)
 	default:
 		utils.Fail(c, http.StatusNotFound, "گفتگو یافت نشد", nil)
 	}

internal/handler/monitoring_handler.go

@@ -0,0 +1,35 @@
+package handler
+
+import (
+	"net/http"
+	"strconv"
+
+	"github.com/gin-gonic/gin"
+
+	"dating-app/internal/monitoring"
+	"dating-app/internal/utils"
+)
+
+type MonitoringHandler struct {
+	store *monitoring.Store
+}
+
+func NewMonitoringHandler(store *monitoring.Store) *MonitoringHandler {
+	return &MonitoringHandler{store: store}
+}
+
+// Summary GET /admin/monitoring/summary
+func (h *MonitoringHandler) Summary(c *gin.Context) {
+	utils.Success(c, http.StatusOK, "", h.store.Summary())
+}
+
+// RecentRequests GET /admin/monitoring/requests?limit=100
+func (h *MonitoringHandler) RecentRequests(c *gin.Context) {
+	limit := 100
+	if raw := c.Query("limit"); raw != "" {
+		if n, err := strconv.Atoi(raw); err == nil && n > 0 && n <= 1000 {
+			limit = n
+		}
+	}
+	utils.Success(c, http.StatusOK, "", h.store.Recent(limit))
+}