Adds a dedicated super admin page for managing idea submissions across
all tenants. Includes status summary cards, filterable/searchable table,
detail modal with status updates, and private admin notes for internal
tracking (sprint refs, thoughts, follow-ups). Notes are not visible to
tenant users.
- Database: admin_note column on shared.ideas (019 migration)
- Backend: PUT /admin/ideas/:id/note endpoint
- Frontend: AdminIdeasPage with table, filters, detail modal
- Sidebar: "Idea Submissions" nav link in admin sections
- Routing: /admin/ideas route under SuperAdminRoute guard
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>