fix(send_message): support Telegram rich messages

[tsale]

Summary

• add an opt-in Telegram sendRichMessage fast path to the standalone send_message tool
• pass raw Markdown to Telegram rich messages so tables, task lists, headings, and other Bot API 10.1 constructs render natively
• fall back to legacy MarkdownV2 only on rich parser/capability failures, while avoiding legacy duplicate sends on transient rich failures
• coerce string config values like "false"/"true" correctly for platforms.telegram.extra.rich_messages

Fixes #45854.

Notes

This keeps the tool/cron path aligned with the gateway rich-message opt-in behavior without changing the default: rich messages remain disabled unless platforms.telegram.extra.rich_messages: true is configured.

Test plan

• uv run --extra dev --extra messaging python -m pytest tests/tools/test_send_message_tool.py -q -o addopts=
• git diff --check
• uv run python -m py_compile tools/send_message_tool.py tests/tools/test_send_message_tool.py

[alt-glitch]

Duplicate of #46118 — both add an opt-in Telegram sendRichMessage fast-path to the standalone send_message tool (Fixes #45854). #46118 is the earliest open same-approach PR. Related: #46263 (same standalone-tool opt-in), #46317 (gateway opt-in).