feat: announcements subsystem (admin + site banner)

[cdcore09]

Summary

Plan 3 of 5 from the events / announcements / forms brainstorm. Lands the announcements admin + the public `` on top of the Plan 1 foundation (#1994) and Plan 2 events patterns (#1998).

Admin API

• `POST/GET /admin/announcements` — create draft + list with filters (status/scope/host/q)
• `GET/PATCH /admin/announcements/:id` — detail (with reviews/comments/audit) + patch gated by `canEditArtifact`
• `POST /admin/announcements/:id/transitions` — wraps `applyTransition` (action set omits `cancel` — announcements have no cancel action, only archive)
• `POST /admin/announcements/:id/comments` — comment endpoint using `sanitizeCommentBody`

Admin UI

• `/admin/announcements` list with status filter + search
• `/admin/announcements/new` compose form (title, body, link URL, expiresAt)
• `/admin/announcements/:id` detail page with Identity / Content / Review / Audit tabs
• Sidebar nav: new Announcements entry at slot 06 (Recognition, Settings, Audit shifted up)

Public UI

• `` mounted in the public app shell above ``. Calls `GET /announcements/active-banner` (already shipped from Plan 1) and renders the banner when one is active. Dismissible per banner-id via localStorage.
• Returns null today since no announcement has a `posted` `site_banner` channel yet — Plan 5 wires the broadcast flow that flips channels to `posted`.

Stats

• 10 commits, atomic, conventional, zero AI attribution
• 18 new vitest tests on top of 216 → 234 total pass
• Full repo typecheck clean

Test plan

• CI green (Cloudflare Pages preview deploys; CircleCI legacy may error — expected)
• Manual: super_admin creates an announcement, submits, second super_admin approves twice — announcement publishes
• Manual: until Plan 5 ships, the banner does not appear (active-banner returns null) — visit `/` and confirm no banner renders
• Manual: announcement with `expiresAt` in the past auto-transitions to `expired` via the Plan 1 `effectiveStatus` read-time logic

Plan + spec

• Spec: `docs/superpowers/specs/2026-05-20-events-announcements-forms-design.md`
• Plan: `docs/superpowers/plans/2026-05-27-announcements-implementation.md`
• Builds on: PR feat(api): artifact subsystem foundation (schema + lifecycle + queue) #1994 (Plan 1 foundation), PR feat: events subsystem (admin + member submit + public) #1998 (Plan 2 events)

Deferred to subsequent plans

• Broadcast tab on announcement detail — Plan 5 (makes banners actually appear via channel approval)
• Attached form section — Plan 4
• Public `/announcements` index page — spec §7.4 defers indefinitely

[cloudflare-workers-and-pages]

Deploying us-rse-admin with    Cloudflare Pages

Latest commit:	8a6334f
Status:	✅  Deploy successful!
Preview URL:	https://a060ab6b.us-rse-admin.pages.dev
Branch Preview URL:	https://cdcore09-announcements-imple.us-rse-admin.pages.dev

View logs

[cloudflare-workers-and-pages]

Deploying usrse-github-io with    Cloudflare Pages

Latest commit:	8a6334f
Status:	✅  Deploy successful!
Preview URL:	https://f6ae3127.usrse-github-io.pages.dev
Branch Preview URL:	https://cdcore09-announcements-imple.usrse-github-io.pages.dev

View logs