Add bio field and daily streak check-in for gamification

- User.Bio: a short (300 char) freeform profile bio, editable via
  PATCH /profile/bio, shown on discover cards and candidate detail (richer
  profiles beyond the fixed onboarding fields).
- User.StreakCount/LastActiveDate: POST /profile/checkin increments the
  streak on consecutive days, resets after a gap, no-ops if already
  checked in today. Backs a daily-return hook on the frontend.

internal/dto/profile_dto.go

@@ -5,3 +5,14 @@ type UpdateLocationRequest struct {
 	Latitude  float64 `json:"latitude" binding:"required"`
 	Longitude float64 `json:"longitude" binding:"required"`
 }
+
+// UpdateBioRequest ویرایش بیوگرافی کوتاه پروفایل
+type UpdateBioRequest struct {
+	Bio string `json:"bio" binding:"max=300"`
+}
+
+// CheckInResult نتیجه‌ی ثبت ورود روزانه (برای استریک گیمیفیکیشن)
+type CheckInResult struct {
+	StreakCount int  `json:"streak_count"`
+	IsNewToday  bool `json:"is_new_today"`
+}