feat(profile): "set your city" gamification box → one-time 500-coin reward

- New searchable city picker (src/lib/iran-cities.ts, ~60 Iranian cities,
  fa/en search) shown as a gold reward card at the top of the profile Basic tab.
- First time a non-empty city is set, the player earns 500 coins (CITY_REWARD),
  granted server-authoritatively. Collapses to a compact summary afterwards with
  a "change city" option (no re-reward).
- Frontend: UserProfile.city + cityRewardClaimed; mock-service grants on first
  set; session/service updateProfile accept `city`; celebratory toast + sfx.
- Backend (.NET): ProfileDto.City/CityRewardClaimed (JSON blob → no migration);
  ProfileService.Update grants +500 once and writes a "city" ledger entry.
- i18n: city.* keys (fa + en).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib/i18n.tsx

@@ -152,6 +152,15 @@ const fa: Dict = {
   "chat.placeholder": "پیام بنویسید…",
   "chat.send": "ارسال",
   "chat.emoji": "ایموجی",
+  "city.rewardTitle": "شهرت را انتخاب کن!",
+  "city.rewardSub": "{n} سکه هدیه بگیر",
+  "city.search": "جستجوی شهر…",
+  "city.none": "شهری پیدا نشد",
+  "city.claim": "ثبت و دریافت {n} سکه",
+  "city.saveCity": "ذخیره: {city}",
+  "city.claimed": "جایزهٔ شهر دریافت شد ✓",
+  "city.change": "تغییر",
+  "city.unknown": "نامشخص",
   "chat.empty": "گفتگو را شروع کنید",
   "friends.message": "پیام",
 
@@ -503,6 +512,15 @@ const en: Dict = {
   "chat.placeholder": "Type a message…",
   "chat.send": "Send",
   "chat.emoji": "Emoji",
+  "city.rewardTitle": "Set your city!",
+  "city.rewardSub": "Earn {n} coins",
+  "city.search": "Search city…",
+  "city.none": "No city found",
+  "city.claim": "Save & get {n} coins",
+  "city.saveCity": "Save: {city}",
+  "city.claimed": "City reward claimed ✓",
+  "city.change": "Change",
+  "city.unknown": "Unknown",
   "chat.empty": "Start the conversation",
   "friends.message": "Message",