[Feat] Enable Slack Agent messaging in generated apps

[mrubens]

Related issue

Internal Roomote work; no linked issue.

Why this PR exists

• I am a maintainer / this is internal Roomote work

Generated Roomote Slack apps were configured as standard bot apps. Slack could accept native streaming API calls while not rendering the Agent task-card experience. Declaring features.agent_view aligns generated apps with Slack's current agent surface.

What changed

• enable Slack's current Agent messaging experience in generated app manifests
• request assistant:write and subscribe to Agent-view context events
• document the one-time update required for manually configured Slack apps

Impact

Newly generated Slack apps can render native agent loading states and streamed task cards. Existing manually configured apps need the Agents feature enabled, the added scope/events, a reinstall, and a Slack hard refresh.

How it was tested

• Slack manifest client tests (9 passed)
• Slack app creation server tests (10 passed)
• @roomote/web typecheck
• targeted ESLint
• docs validation

Checklist

• The PR title follows the repo convention
• This PR is small and scoped to one change
• Full-repo pnpm lint and pnpm check-types (focused checks are listed above)
• I added tests and included validation notes above
• I removed secrets, tokens, private keys, and customer data
• Changelog entry (not included in this scoped PR)

[roomote-community]

1 issue outstanding. See task

• Add the Slack Agent response loop so Agent View opens the thread and renders native loading and streamed task states.

_{Reviewed 7f1bbd1}

[roomote-community]

Enabling agent_view alone does not activate the response loop this PR documents. The current Slack client only posts ordinary messages; it never calls assistant.threads.setStatus (required after message.im to open the Agent thread and show its loading state) or the chat.*Stream methods needed for streamed task cards. Generated apps will therefore be switched to the Agent surface without the native loading/thread behavior claimed here. Please add the Agent response calls before enabling this manifest feature, or limit the change and documentation to the surface migration.