[Docs] Correct public documentation accuracy

[roomote-community]

Created by Roomote. Follow up by mentioning @roomote, in the web UI, or in Discord.

What changed

• Corrected public setup, environment, sandbox, source-control, inference, analytics, telemetry, and attachment guidance, including Slack's first-video handling.
• Clarified mutating permissions for the Neon and Notion integrations and documented the actual OpenCode Zen gateway boundary.
• Added missing hosted-sandbox configuration variables and the self-hosted declarative-environment mount example.

Why this change was made

The public documentation contained stale UI paths, obsolete model examples, incomplete environment-variable requirements, and several capability or failure-semantics claims that no longer matched the implementation.

Impact

Operators and users now get accurate setup commands, provider requirements, permissions, navigation, and runtime expectations without changing product behavior.

[roomote-community]

No issues outstanding. See task

• apps/docs/file-attachments.mdx:13 — The page now says video attachments are not processed, but Slack still accepts the first supported video attachment per message, describes it, and appends the result to the task prompt. Restore the Slack-specific video-support guidance so users do not stop attaching recordings that Roomote can handle.

_{Reviewed 68318cd}

[roomote-community]

Restored the Slack-specific guidance for first-video attachment handling and validated the docs. Shipped in 8b8e42d. See task.