[Feat] Add Goal Mode commands across chat providers

[roomote-roomote]

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

What changed

• Added one canonical /goal <objective> parser shared by communication providers.
• Enabled Goal Mode from Slack, Teams, Telegram, and Discord on both fresh launches and active task follow-ups.
• Registered native Telegram and Discord command entries while preserving provider-specific addressing rules; Slack uses typed /goal messages inside task threads because native slash-command payloads do not identify a task thread.
• Carried trusted goal generations through durable provider queues and preserved Goal Mode through routing-confirmation flows.
• Added focused coverage for parsing, provider registration, fresh launch propagation, and activation rollback.

Why this change was made

Goal Mode previously worked only in the existing-task web prompt. Communication providers treated /goal as ordinary text, creating inconsistent behavior and leaving each provider to invent command semantics independently.

Impact

Users can now start or replace a Goal Mode objective from Slack, Teams, Telegram, or Discord. Active-task activation remains atomic on delivery failure: failed delivery rolls back the pending goal instead of leaving a task in a partially enabled state. Slack no longer exposes a native slash command that could silently start a second task instead of addressing the active thread. The web home composer remains unchanged by design.

[roomote-community]

No code issues found. See task

• Slack native /goal commands in an active task thread create a second task rather than enabling Goal Mode on the existing task (apps/api/src/handlers/slack/index.ts:127). Fixed in 36382791 by removing the unaddressed native slash-command path and keeping Slack /goal in task threads.

_{Reviewed 3638279}

[roomote-roomote]

Fixed the Slack native-command issue in 36382791: /goal stays inside task threads instead of launching a second task from an unaddressed slash payload. The failed worker proxy test passed locally (51/51) without code changes, confirming the CI failure was unrelated/flaky. Targeted Slack/web suites, lint, and repository type checks pass.