Phase 1c — Promote + composer + Social page

Phase 1c of Kazokus Social Publishing completes the customer-facing experience. Community admins can now click Promote on any thread, article, or event, edit the draft in a composer drawer (with per-channel selection and capacity indicators), submit for review, then approve from a dedicated Social page where all drafts live in a three-tab layout (Needs review / Scheduled / All).

Consumes the backend API from #549 / #550 plus the Phase 1b settings UI from #551 / #552.