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>

app/backend/internal/cli/commands/auth.go

@@ -147,5 +147,21 @@ func runStatus(cmd *cobra.Command, args []string) error {
 	if p.IsAdmin {
 		fmt.Println("Role:     platform admin")
 	}
+
+	var bannersResp struct {
+		Banners []struct {
+			Title string `json:"title"`
+			Body  string `json:"body"`
+			Level string `json:"level"`
+		} `json:"banners"`
+	}
+	if err := client.DoJSON("GET", "/banners/active", nil, &bannersResp); err == nil {
+		for _, b := range bannersResp.Banners {
+			fmt.Printf("[%s] %s\n", b.Level, b.Title)
+			if b.Body != "" {
+				fmt.Printf("      %s\n", b.Body)
+			}
+		}
+	}
 	return nil
 }