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/online/gamification.ts

@@ -803,3 +803,8 @@ export const DAILY_REWARDS = [100, 150, 200, 300, 400, 600, 1500];
 export function dailyRewardFor(day: number): number {
   return DAILY_REWARDS[Math.min(day, DAILY_REWARDS.length) - 1] ?? 100;
 }
+
+/* ----------------------- Profile-completion reward ----------------------- */
+
+/** One-time coin reward for setting your city on the profile. */
+export const CITY_REWARD = 500;