feat: add /admin command to list room admins

Implement /admin command as specified in issue #50:
- Lists all admin user IDs for the current room
- Output format: 'Room Admins:\n- @user1\n- @user2'
- Shows 'No admins configured for this room.' if none exist
- Available to everyone (no permission check needed)

Changes:
- Add _find_username_by_user_id helper function
- Update cmd_admin to support listing when called with no args
- Update /help to include /admin command

Closes #50

apps/telegram-bot/commands.py

@@ -502,11 +502,42 @@ def _find_user_id_by_username(room_id: int, username: str) -> int | None:
     return None
 
 
+def _find_username_by_user_id(room_id: int, user_id: int) -> str | None:
+    """Find username by user_id from bounty creators in the room."""
+    bounties = BOUNTY_SERVICE.list_bounties(room_id)
+    for bounty in bounties:
+        if bounty.created_by_user_id == user_id:
+            return bounty.created_by_username
+    return None
+
+
 async def cmd_admin(update: Update, ctx: ContextTypes.DEFAULT_TYPE) -> None:
     args = extract_args(update.message.text)
-    if not args or args[0] not in ("add", "remove"):
+
+    # Handle /admin with no subcommand (list admins)
+    if not args or args[0] == "list":
+        room_id = get_room_id(update)
+        admin_ids = BOUNTY_SERVICE.list_admins(room_id)
+
+        if not admin_ids:
+            await update.message.reply_text("No admins configured for this room.")
+            return
+
+        lines = ["Room Admins:"]
+        for admin_id in admin_ids:
+            username = _find_username_by_user_id(room_id, admin_id)
+            if username:
+                lines.append(f"- @{username}")
+            else:
+                lines.append(f"- user#{admin_id}")
+
+        await update.message.reply_text("\n".join(lines))
+        return
+
+    if args[0] not in ("add", "remove"):
         await update.message.reply_text(
             "Usage:\n"
+            "/admin — list admins\n"
             "/admin add @username — add admin\n"
             "/admin remove @username — remove admin"
         )
@@ -565,6 +596,9 @@ async def cmd_help(update: Update, ctx: ContextTypes.DEFAULT_TYPE) -> None:
         "/show <id> — show bounty details\n"
         "/timezone — get room timezone\n"
         "/timezone <tz> — set room timezone (admin only)\n"
+        "/admin — list room admins\n"
+        "/admin add @username — add admin (admin only)\n"
+        "/admin remove @username — remove admin (admin only)\n"
         "/start — re-initialize\n"
         "/help — this message",
         disable_web_page_preview=True,