[Feat] Add resumable stop commands for chat sessions

[roomote-roomote]

​Opened on behalf of @daniel-lxs. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Add /stop commands for Discord and Telegram, message-based stop handling for Slack and Microsoft Teams, and provider help/documentation.
• Recognize a bare stop reply in an existing Slack channel session thread; a bare stop outside a stoppable session thread is ignored.
• Stop every active task linked to the current session through the same resumable soft-stop path used by the web Stop tasks action, including delegated child tasks.
• Resolve the session by the exact provider conversation/thread or reply binding and require the linked session owner; leave unrelated or inaccessible sessions untouched.
• Share the stop implementation with the web action so chat and web have the same task selection and race handling.

Why this change was made

People can interrupt active session tasks from the chat conversation without permanently canceling the work or stopping child tasks one by one.

Impact

The session owner can stop all currently active linked tasks from Slack, Discord, Telegram, or Teams and continue later with another message. In Slack, an owner can reply stop in the session thread without mentioning the app; other users cannot stop that owner's tasks. Tasks that fail to stop are reported rather than represented as successfully stopped. Communication, SDK, and API type checks plus the web fast type check passed; the full web type check exceeded the local command time limit.

[roomote-community]

No new code issues found. See task

• Slack: bare stop replies in an existing channel session thread bypass the stop handler because the new routing predicate requires a bot mention.

_{Reviewed 9d1ae25}

[roomote-roomote]

Fixed Slack stop routing so a linked owner’s bare stop reply in an existing session thread reaches the resumable stop handler; bare stops outside a stoppable session and stops from other users remain non-mutating. Pushed commit 9d1ae255.

The Roomote code review check now passes with no new code issues, and the finding is checked in the review summary with its thread resolved. The PR Test, Type Check, Lint, Knip, and docs checks also pass.