feat(telegram): per-chat command localization + unified locale resolver

Two related Telegram changes:

1. Per-chat command localization. setMyCommands now accepts a scope
   (BotCommandScopeChat) and deleteMyCommands clears scoped bindings.
   Command registration runs three tiers: default → per-language
   (Telegram client language) → per-chat (UI override). Saving a
   chat's language_override or commands_enabled toggle pushes the
   binding to Telegram inline rather than waiting on the 30s
   debounced bot-wide sync.

2. Unified Telegram locale resolution. Three test paths (bot test_chat,
   target receiver test, target-level fan-out) used to disagree on
   locale priority — the target receiver test in particular only
   consulted receiver.locale and ignored the chat's language_override.
   Introduced pick_telegram_locale (pure) and
   resolve_telegram_chat_locale (async DB lookup) in services/notifier
   so all three paths share one priority order:

       receiver.locale → chat.language_override → chat.language_code → fallback

   Fan-out keeps batch-loading TelegramChat rows for efficiency, just
   runs them through the same priority function now.

packages/server/src/notify_bridge_server/api/target_receivers.py

@@ -11,7 +11,11 @@ from sqlmodel.ext.asyncio.session import AsyncSession
 from ..auth.dependencies import get_current_user
 from ..database.engine import get_session
 from ..database.models import NotificationTarget, TargetReceiver, User
-from ..services.notifier import send_to_receiver
+from ..services.notifier import (
+    _get_test_message,
+    resolve_telegram_chat_locale,
+    send_to_receiver,
+)
 from .helpers import get_owned_entity
 
 _LOGGER = logging.getLogger(__name__)
@@ -130,14 +134,28 @@ async def test_receiver(
     user: User = Depends(get_current_user),
     session: AsyncSession = Depends(get_session),
 ):
-    """Send a test notification to a single receiver."""
+    """Send a test notification to a single receiver.
+
+    For Telegram targets, locale resolution goes through the shared
+    ``resolve_telegram_chat_locale`` helper so the per-chat ``language_override``
+    set in the bot manager is respected here too — previously this endpoint
+    only consulted ``receiver.locale`` and ignored chat-side overrides.
+    """
     target = await _get_user_target(session, target_id, user.id)
     receiver = await session.get(TargetReceiver, receiver_id)
     if not receiver or receiver.target_id != target_id:
         raise HTTPException(status_code=404, detail="Receiver not found")
 
-    from ..services.notifier import _get_test_message
-    effective_locale = getattr(receiver, 'locale', '') or locale
+    if target.type == "telegram":
+        effective_locale = await resolve_telegram_chat_locale(
+            session,
+            bot_id=target.config.get("bot_id"),
+            chat_id=receiver.config.get("chat_id"),
+            receiver=receiver,
+            fallback=locale,
+        )
+    else:
+        effective_locale = (getattr(receiver, "locale", "") or locale)[:2].lower()
     message = _get_test_message(effective_locale, target.type)
     return await send_to_receiver(target, dict(receiver.config), message)