[Improve] Update Slack app manifests from settings

[mrubens]

Summary

• add an Update app action for connected Slack apps in Communication Settings
• export, reconcile, validate, and update the manifest with a one-time app configuration token while preserving custom fields
• guide admins through Slack reinstallation when updated permissions require approval
• extend the mock Slack harness and public setup documentation for manifest updates

Testing

• pnpm --filter @roomote/web exec vitest run --project server src/trpc/commands/slack/update-app-manifest.test.ts
• pnpm --filter @roomote/web exec vitest run --project client src/components/settings/SlackManifestUpdateDialog.test.tsx src/components/settings/CommsProviderSection.test.tsx
• pnpm --filter @roomote/slack exec vitest run src/__tests__/mock-slack-server.test.ts
• pnpm --filter @roomote/web check-types
• pnpm --filter @roomote/slack check-types
• pnpm --filter @roomote/web lint
• pnpm --filter @roomote/slack lint
• pnpm --filter @roomote/docs check

[roomote-community]

No code issues found. See task

_{Reviewed 86d33b6}