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.

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

app/backend/sqlc/queries/banners.sql

@@ -0,0 +1,39 @@
+-- name: ListBanners :many
+SELECT banners.*
+FROM banners
+ORDER BY created_at DESC;
+
+-- name: ListActiveBanners :many
+SELECT banners.*
+FROM banners
+WHERE active
+  AND (starts_at IS NULL OR starts_at <= now())
+  AND (ends_at IS NULL OR ends_at > now())
+ORDER BY created_at DESC;
+
+-- name: GetBannerByID :one
+SELECT banners.*
+FROM banners
+WHERE id = $1;
+
+-- name: CreateBanner :one
+INSERT INTO banners (title, body, level, active, dismissible, created_by, starts_at, ends_at)
+VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
+RETURNING banners.*;
+
+-- name: UpdateBanner :one
+UPDATE banners
+SET title = $2,
+    body = $3,
+    level = $4,
+    active = $5,
+    dismissible = $6,
+    starts_at = $7,
+    ends_at = $8,
+    updated_at = now()
+WHERE id = $1
+RETURNING banners.*;
+
+-- name: DeleteBanner :exec
+DELETE FROM banners
+WHERE id = $1;

app/backend/sqlc/schema.sql

@@ -302,3 +302,17 @@ CREATE TABLE webhook_deliveries (
     created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
     delivered_at TIMESTAMP WITH TIME ZONE
 );
+
+CREATE TABLE banners (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    title VARCHAR(255) NOT NULL,
+    body TEXT NOT NULL DEFAULT '',
+    level VARCHAR(20) NOT NULL DEFAULT 'info',
+    active BOOLEAN NOT NULL DEFAULT true,
+    dismissible BOOLEAN NOT NULL DEFAULT true,
+    created_by UUID REFERENCES users(id) ON DELETE SET NULL,
+    starts_at TIMESTAMP WITH TIME ZONE,
+    ends_at TIMESTAMP WITH TIME ZONE,
+    created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
+    updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
+);