feat: implement /timezone command to get/set room timezone

- Add cmd_timezone handler for /timezone command
- Validate timezone using IANA format (zoneinfo.ZoneInfo)
- Use existing BountyService.get_timezone and set_timezone methods
- Admin-only permission via service layer
- Update help text and bot command list
- Fixes #53

apps/telegram-bot/commands.py

@@ -3,6 +3,7 @@
 import time
 from functools import wraps
 from typing import Optional
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
 
 import dateparser
 from telegram import Update
@@ -323,7 +324,37 @@ async def cmd_help(update: Update, ctx: ContextTypes.DEFAULT_TYPE) -> None:
         "/delete <id> — delete bounty\n"
         "/track <id> — track a bounty (groups only)\n"
         "/untrack <id> — stop tracking (groups only)\n"
+        "/timezone [tz] — get/set room timezone (admin only)\n"
         "/start — re-initialize\n"
         "/help — this message",
         disable_web_page_preview=True,
     )
+
+
+async def cmd_timezone(update: Update, ctx: ContextTypes.DEFAULT_TYPE) -> None:
+    args = extract_args(update.message.text)
+    room_id = get_room_id(update)
+    user_id = get_user_id(update)
+
+    if not args:
+        current_tz = BOUNTY_SERVICE.get_timezone(room_id)
+        await update.message.reply_text(f"Current timezone: {current_tz}")
+        return
+
+    timezone_str = args[0]
+
+    try:
+        ZoneInfo(timezone_str)
+    except (KeyError, ZoneInfoNotFoundError):
+        await update.message.reply_text(
+            "⛔ Invalid timezone. Use IANA format (e.g., Asia/Jakarta)"
+        )
+        return
+
+    try:
+        BOUNTY_SERVICE.set_timezone(room_id, timezone_str, user_id)
+    except PermissionError as e:
+        await update.message.reply_text(f"⛔ {e}")
+        return
+
+    await update.message.reply_text(f"✅ Timezone set to {timezone_str}.")