feat: Telegram send_document and send_video for native file attachments

Implement send_document() and send_video() overrides in TelegramAdapter
so the agent can deliver files (PDFs, CSVs, docs, etc.) and videos as
native Telegram attachments instead of just printing the file path as
text.

The base adapter already routes MEDIA:<path> tags by extension — audio
goes to send_voice(), images to send_image_file(), and everything else
falls through to send_document(). But TelegramAdapter didn't override
send_document() or send_video(), so those fell back to plain text.

Now when the agent includes MEDIA:/path/to/report.pdf in its response,
users get a proper downloadable file attachment in Telegram.

Features:
- send_document: sends files via bot.send_document with display name,
  caption (truncated to 1024), and reply_to support
- send_video: sends videos via bot.send_video with inline playback
- Both fall back to base class text if the Telegram API call fails
- 10 new tests covering success, custom filename, file-not-found,
  not-connected, caption truncation, API error fallback, and reply_to

Requested by @TigerHixTang on Twitter.

gateway/platforms/telegram.py

@@ -346,6 +346,64 @@ class TelegramAdapter(BasePlatformAdapter):
             print(f"[{self.name}] Failed to send local image: {e}")
             return await super().send_image_file(chat_id, image_path, caption, reply_to)
 
+    async def send_document(
+        self,
+        chat_id: str,
+        file_path: str,
+        caption: Optional[str] = None,
+        file_name: Optional[str] = None,
+        reply_to: Optional[str] = None,
+    ) -> SendResult:
+        """Send a document/file natively as a Telegram file attachment."""
+        if not self._bot:
+            return SendResult(success=False, error="Not connected")
+
+        try:
+            if not os.path.exists(file_path):
+                return SendResult(success=False, error=f"File not found: {file_path}")
+
+            display_name = file_name or os.path.basename(file_path)
+
+            with open(file_path, "rb") as f:
+                msg = await self._bot.send_document(
+                    chat_id=int(chat_id),
+                    document=f,
+                    filename=display_name,
+                    caption=caption[:1024] if caption else None,
+                    reply_to_message_id=int(reply_to) if reply_to else None,
+                )
+            return SendResult(success=True, message_id=str(msg.message_id))
+        except Exception as e:
+            print(f"[{self.name}] Failed to send document: {e}")
+            return await super().send_document(chat_id, file_path, caption, file_name, reply_to)
+
+    async def send_video(
+        self,
+        chat_id: str,
+        video_path: str,
+        caption: Optional[str] = None,
+        reply_to: Optional[str] = None,
+    ) -> SendResult:
+        """Send a video natively as a Telegram video message."""
+        if not self._bot:
+            return SendResult(success=False, error="Not connected")
+
+        try:
+            if not os.path.exists(video_path):
+                return SendResult(success=False, error=f"Video file not found: {video_path}")
+
+            with open(video_path, "rb") as f:
+                msg = await self._bot.send_video(
+                    chat_id=int(chat_id),
+                    video=f,
+                    caption=caption[:1024] if caption else None,
+                    reply_to_message_id=int(reply_to) if reply_to else None,
+                )
+            return SendResult(success=True, message_id=str(msg.message_id))
+        except Exception as e:
+            print(f"[{self.name}] Failed to send video: {e}")
+            return await super().send_video(chat_id, video_path, caption, reply_to)
+
     async def send_image(
         self,
         chat_id: str,