Slack workspace management moved to an admin-only ops page

Slack workspace management has moved from account settings to a dedicated admin-only /ops/slack page. Instance admins now install, connect, and disconnect Slack workspaces from the new ops area, while regular users retain the ability to create forage items from Slack messages and receive bot replies in threads. The /ops route redirects to /ops/slack, and Slack install, callback, and disconnect actions are gated behind the instance admin role.