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/utils/age_test.go

@@ -0,0 +1,26 @@
+package utils
+
+import (
+	"testing"
+	"time"
+)
+
+func TestCalcAge_NilBirthDate(t *testing.T) {
+	if age := CalcAge(nil); age != 0 {
+		t.Fatalf("expected 0 for nil birth date, got %d", age)
+	}
+}
+
+func TestCalcAge_BirthdayAlreadyPassedThisYear(t *testing.T) {
+	birth := time.Now().AddDate(-25, -1, 0) // ۲۵ سال و ۱ ماه پیش -> تولد امسال رد شده
+	if age := CalcAge(&birth); age != 25 {
+		t.Fatalf("expected age 25, got %d", age)
+	}
+}
+
+func TestCalcAge_BirthdayNotYetThisYear(t *testing.T) {
+	birth := time.Now().AddDate(-25, 1, 0) // تولد ۱ ماه دیگه‌ست -> هنوز ۲۴ سالشه
+	if age := CalcAge(&birth); age != 24 {
+		t.Fatalf("expected age 24, got %d", age)
+	}
+}