feat: Telegram bot — full functionality with inline keyboards, file upload, auth

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/messengers/base.py

@@ -0,0 +1,24 @@
+from abc import ABC, abstractmethod
+from typing import Any
+
+
+class MessengerService(ABC):
+    @abstractmethod
+    async def setup(self):
+        pass
+
+    @abstractmethod
+    async def shutdown(self):
+        pass
+
+    @abstractmethod
+    async def send_message(self, chat_id: str, text: str, **kwargs):
+        pass
+
+    @abstractmethod
+    async def send_file(self, chat_id: str, file_path: str, caption: str = ""):
+        pass
+
+    @abstractmethod
+    async def notify_progress(self, chat_id: str, status: str, progress: int | None = None):
+        pass