feat(banners): instance announcements — admin CRUD, top bar, CLI (#39)

banners table (title/body/level/active/dismissible/schedule window).
GET /banners/active for signed-in users; admin CRUD under /admin/banners.
BannerBar renders above the header with per-banner dismissal
(localStorage); admin console gains an Announcements section;
`containr banners` manages them and `auth status` prints active ones.

Generated with [Devin](https://devin.ai)

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

ROADMAP2.md

@@ -284,8 +284,11 @@ and wired refs, one click or one CLI call.
   CLI + MCP + `/settings/webhooks` page with delivery log + test ping.
 - [ ] **Activity feed** — enrich `audit_logs` with `severity category
   icon label metadata`; per-project timeline + global feed; TTL job.
-- [ ] **Banners** — `banners(title, body, level, scope, active)`; top
-  bar in UI + surfaced to CLI on `auth status`.
+- [x] **Banners** — `banners` table with title/body/level/active/
+  dismissible/schedule window. `GET /banners/active` for signed-in
+  users; admin CRUD at `/admin/banners`. `BannerBar` renders above the
+  header (per-banner dismiss via localStorage); admin console manages
+  them; `containr banners` CLI + `auth status` surfaces active ones.
 - [ ] **White-label** — `app_settings.branding`: product name, logos,
   favicon, accent override, docs/support links. `GET /api/v1/branding`
   public + cached. **Containr/Vertice remains default;** this is for