feat: add plugin-extensible Telegram callbacks

[hampsterx]

Summary

• add namespaced Telegram callback registration to PluginContext
• route authorized plugin callbacks without overriding built-in controls
• provide dispatch_callback_text() for callback-to-agent session continuity
• document the API and cover registration, authorization, failure isolation, and Telegram topic normalization

Verification

• PYTHONPATH=. python3 -m pytest -o addopts='' tests/hermes_cli/test_plugins.py tests/gateway/test_telegram_approval_buttons.py -q (150 passed)
• ruff check on all changed Python files
• independent Codex review: PASS

[hampsterx]

Closing as a duplicate. I should have searched the existing issue/PR set before opening this.

Closest existing work:

• feat(telegram): plugin callback-query handler registration #78619 — near-identical register_telegram_callback_handler API
• feat(plugins): add Telegram callback query hook #80458 — generic authenticated Telegram callback-query hook
• feat(plugins): add register_telegram_handler plugin API (mirrors Slack) #61576 / feat(plugins): let plugins register Telegram PTB handlers (ctx.register_telegram_handler) #59159 — broader PTB handler registration APIs
• feat(telegram): add plugin-owned callback actions #65255 — plugin-owned callback actions and cron-delivery buttons
• [Feature]: Add pre_callback_query_dispatch plugin hook for Telegram inline keyboard callbacks #21469 — original callback-dispatch extension issue

This branch also includes a callback-to-normal-message helper for session continuity, but that incremental need is better discussed on the existing consolidation path rather than carried as another competing callback API. I am keeping the branch only for the local deployed plugin while upstream converges.