[Fix] Request Agent scope during Slack installs

[mrubens]

Related issue

Internal Roomote work; no linked issue.

Why this PR exists

• I am a maintainer / this is internal Roomote work

The generated Slack app manifest and the OAuth installer maintained separate hard-coded bot-scope lists. After Agent messaging added assistant:write to the manifest, the install URL continued requesting the older list, so newly installed bot tokens did not receive the Agent scope.

What changed

• build Slack installation URLs from the manifest's canonical bot scopes
• remove the duplicated scope list from the Slack connection command
• add regression coverage proving OAuth installs request assistant:write

Impact

Generated Slack apps now receive the same scopes during OAuth installation that their manifests declare, enabling Slack's Agent messaging APIs after reinstalling the app.

How it was tested

• Slack install URL and manifest client tests (10 passed)
• @roomote/web typecheck
• targeted ESLint
• focused formatting check

Checklist

• The PR title follows the repo convention
• This PR is small and scoped to one change
• Focused lint and typecheck pass locally
• I added tests and included validation notes above
• I removed secrets, tokens, private keys, and customer data
• Changelog entry (not included in this scoped fix)

[roomote-community]

No code issues found. See task

_{Reviewed 6da1cd7}