Expose Telegram bot commands in the native slash menu

[yaroslav-upriver]

Description

Telegram currently supports the available bot commands, but they are only discoverable if the user manually types help.

This feature should expose the existing command set through Telegram's native slash-command UI so commands appear in the standard menu when the user taps /. It should also improve /agent so that sending it without an argument returns the current list of available agents from the server.

Alternatives Considered

• Keep relying on /help only. This keeps the implementation simple, but it hides functionality behind a manual text command and does not match the standard Telegram bot experience.
• Add dynamic argument autocomplete for /agent <name>. Telegram Bot API does not support server-driven autocomplete for command arguments, so this is not a practical option here.

Additional Context

Proposed behavior:

• Register Telegram bot commands with setMyCommands during bot startup.
• Reuse a unified command catalog so the same command definitions power Telegram slash commands, /help, and /api/commands.
• Make /agent without arguments return usage guidance plus the live agent list fetched from the server.

This keeps command discovery consistent across Telegram and the existing API/help surfaces while staying within current Telegram Bot API capabilities.

[jaberjaber23]

Telegram bot commands can be registered via BotFather's /setcommands. OpenFang could auto-register them by calling the Telegram setMyCommands API on adapter startup. This is a feature request for the Telegram adapter.