#13070: feat: Add support for custom Telegram Bot API server URL via apiRoot option

add apiRoot and docs <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR adds an `apiRoot` option to Telegram account configuration and wires it into the grammY `Bot` client options, allowing the Telegram channel to target a custom Telegram Bot API base URL (e.g., local Bot API server or proxy). It also updates the English and zh-CN Telegram docs to document the new `channels.telegram.apiRoot` setting and its default (`https://api.telegram.org`). <h3>Confidence Score: 5/5</h3> - This PR appears safe to merge with minimal risk. - Changes are small, isolated to Telegram config/types, bot client construction, and docs. The new option is optional and only affects behavior when explicitly set, so default behavior remains unchanged. - No files require special attention <!-- greptile_other_comments_section --> _{(3/5) Reply to the agent's comments like "Can you suggest a fix for this @greptileai?" or ask follow-up questions!} <!-- /greptile_comment -->