feat: Receiver OOP hierarchy with per-receiver locale resolution

- Introduce Receiver base class + typed subclasses (TelegramReceiver,
  WebhookReceiver, EmailReceiver, etc.) in core/notifications/receiver.py
- Dispatcher uses typed Receiver objects instead of raw dicts, with
  per-receiver locale-aware template rendering
- load_link_data resolves locale from TelegramChat.language_override at
  load time: TargetReceiver.locale || chat.language_override || chat.language_code
- Add language_override field to TelegramChat (separate from auto-detected
  language_code), with per-chat commands toggle and command dispatch using
  override language
- Add locale field to TargetReceiver for explicit per-receiver overrides

packages/server/src/notify_bridge_server/services/dispatch_helpers.py

@@ -10,6 +10,7 @@ from sqlmodel import select
 from sqlmodel.ext.asyncio.session import AsyncSession
 
 from notify_bridge_core.models.events import ServiceEvent
+from notify_bridge_core.notifications.receiver import Receiver, build_receiver
 
 from ..database.models import (
     EmailBot,
@@ -17,6 +18,8 @@ from ..database.models import (
     NotificationTarget,
     NotificationTrackerTarget,
     TargetReceiver,
+    TelegramBot,
+    TelegramChat,
     TemplateConfig,
     TemplateSlot,
     TrackingConfig,
@@ -115,14 +118,44 @@ async def load_link_data(
         if not target:
             continue
 
-        # Load receivers
+        # Load receivers as typed Receiver objects
         recv_result = await session.exec(
             select(TargetReceiver).where(
                 TargetReceiver.target_id == target.id,
                 TargetReceiver.enabled == True,
             )
         )
-        receivers = [dict(r.config) for r in recv_result.all()]
+        recv_rows = recv_result.all()
+
+        # For Telegram targets, resolve locale from TelegramChat
+        chat_locale_map: dict[str, str] = {}
+        if target.type == "telegram":
+            bot_id = target.config.get("bot_id")
+            if bot_id:
+                chat_ids = [str(r.config.get("chat_id", "")) for r in recv_rows if r.config.get("chat_id")]
+                if chat_ids:
+                    chat_result = await session.exec(
+                        select(TelegramChat).where(
+                            TelegramChat.bot_id == bot_id,
+                            TelegramChat.chat_id.in_(chat_ids),
+                        )
+                    )
+                    for chat in chat_result.all():
+                        resolved = (
+                            getattr(chat, 'language_override', '') or
+                            getattr(chat, 'language_code', '') or ''
+                        )
+                        if resolved:
+                            chat_locale_map[chat.chat_id] = resolved[:2].lower()
+
+        receivers: list[Receiver] = []
+        for r in recv_rows:
+            explicit_locale = getattr(r, 'locale', '') or ''
+            locale = explicit_locale
+            if not locale and target.type == "telegram":
+                chat_id = str(r.config.get("chat_id", ""))
+                locale = chat_locale_map.get(chat_id, "")
+            receivers.append(build_receiver(target.type, dict(r.config), locale))
 
         tracking_config = None
         if tt.tracking_config_id: