[Docs] Document recent user-facing behavior

[roomote-community]

​Opened on behalf of @mrubens. View the task or mention @roomote for follow-up asks.

What changed

Updated the public docs to cover user-facing behavior merged during the latest 24-hour review window:

• Goal Mode invocation, continuation limits, blocker handling, and attachment constraints
• connected-system investigations and explicit external actions
• resumable chat threads after provider errors
• outbound Slack DMs to linked workspace users
• provider-neutral video-description model requirements
• OpenCode Go usage-window reporting

Why this change was made

Several shipped capabilities and recovery paths were missing or only indirectly described in the public documentation. This keeps operator and user guidance aligned with the behavior currently on develop.

Impact

Users can now find the practical boundaries and recovery steps for these features in the existing task, communications, attachment, and inference-provider guides. There is no product runtime change.

[roomote-community]

No new code issues found. See task

• apps/docs/file-attachments.mdx:41 now states that Roomote accepts any configured model reporting video input capability.

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