feat: support Telegram image and file sending with captions

[eeee0717]

Summary

This PR adds outbound Telegram attachment sending and makes it usable from agent tool calls.

What changed

• add Telegram image sending for OutboundMessage.MediaPaths
• add Telegram file/document sending for OutboundMessage.FilePaths
• auto-route single images to sendPhoto
• auto-route multiple images to sendMediaGroup
• auto-route single files to sendDocument
• auto-route multiple files to sendMediaGroup(InputMediaDocument)
• split large image/file batches above Telegram's media group limit
• use Text as the attachment caption/message when supported
• send overflow text as a follow-up message when it exceeds Telegram caption limits
• reject unsupported attachment combinations such as EditMsgID, inline buttons, or mixed image+file payloads
• validate local image and file paths before sending
• remove implicit Telegram media-group fallback; grouped sends now fail fast instead of silently degrading to independent messages

Agent/tooling updates

• extend the message tool to support media_paths and file_paths
• allow message tool calls to default to the current conversation route
• inject current channel, account_id, and chat_id into tool execution context
• add FILE: protocol support alongside the existing MEDIA: protocol for tool output attachment sending
• update workspace prompt docs so the agent prefers message with media_paths / file_paths for local attachments

Testing

Manual verification

• sent a single local image to Telegram successfully
• sent multiple local images to Telegram successfully
• sent a single local file to Telegram successfully
• sent multiple local files as grouped documents successfully
• verified local image/file sending can now be invoked through agent tooling in the current conversation