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/banners.go

@@ -0,0 +1,133 @@
+package commands
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+)
+
+var (
+	bannerTitle  string
+	bannerLevel  string
+	bannerBody   string
+	bannerActive bool
+)
+
+// BannersCmd manages instance-wide announcement banners (admin).
+var BannersCmd = &cobra.Command{
+	Use:   "banners",
+	Short: "Manage announcement banners (admin)",
+}
+
+var bannerListCmd = &cobra.Command{
+	Use:   "list",
+	Short: "List all banners",
+	RunE: func(cmd *cobra.Command, args []string) error {
+		c, err := client()
+		if err != nil {
+			return err
+		}
+		data, err := c.Do("GET", "/admin/banners", nil)
+		if err != nil {
+			return err
+		}
+		items, err := unwrapList(data, "banners")
+		if err != nil {
+			return err
+		}
+		rows := make([][]string, 0, len(items))
+		for _, b := range items {
+			rows = append(rows, []string{
+				str(b, "id"), str(b, "title"), str(b, "level"), str(b, "active"),
+			})
+		}
+		printRows(data, []string{"ID", "TITLE", "LEVEL", "ACTIVE"}, rows)
+		return nil
+	},
+}
+
+var bannerCreateCmd = &cobra.Command{
+	Use:   "create <title>",
+	Short: "Create a banner (--body --level info|success|warning|error)",
+	Args:  cobra.ExactArgs(1),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		c, err := client()
+		if err != nil {
+			return err
+		}
+		req := map[string]interface{}{"title": args[0]}
+		if cmd.Flags().Changed("body") {
+			req["body"] = bannerBody
+		}
+		if cmd.Flags().Changed("level") {
+			req["level"] = bannerLevel
+		}
+		data, err := c.Do("POST", "/admin/banners", req)
+		if err != nil {
+			return err
+		}
+		PrintRaw(data)
+		return nil
+	},
+}
+
+var bannerUpdateCmd = &cobra.Command{
+	Use:   "update <id>",
+	Short: "Update a banner (--title --body --level --active/--inactive)",
+	Args:  cobra.ExactArgs(1),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		c, err := client()
+		if err != nil {
+			return err
+		}
+		req := map[string]interface{}{}
+		if cmd.Flags().Changed("title") {
+			req["title"] = bannerTitle
+		}
+		if cmd.Flags().Changed("body") {
+			req["body"] = bannerBody
+		}
+		if cmd.Flags().Changed("level") {
+			req["level"] = bannerLevel
+		}
+		if cmd.Flags().Changed("active") {
+			req["active"] = bannerActive
+		}
+		if len(req) == 0 {
+			return fmt.Errorf("nothing to update — pass --title/--body/--level/--active")
+		}
+		data, err := c.Do("PATCH", "/admin/banners/"+args[0], req)
+		if err != nil {
+			return err
+		}
+		PrintRaw(data)
+		return nil
+	},
+}
+
+var bannerDeleteCmd = &cobra.Command{
+	Use:   "delete <id>",
+	Short: "Delete a banner",
+	Args:  cobra.ExactArgs(1),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		if !Confirm("Delete banner " + args[0] + "?") {
+			return &APIError{Message: "aborted (pass --yes to skip confirmation)", ExitCode: ExitError}
+		}
+		c, err := client()
+		if err != nil {
+			return err
+		}
+		_, err = c.Do("DELETE", "/admin/banners/"+args[0], nil)
+		return err
+	},
+}
+
+func init() {
+	bannerCreateCmd.Flags().StringVar(&bannerBody, "body", "", "banner body text")
+	bannerCreateCmd.Flags().StringVar(&bannerLevel, "level", "info", "info|success|warning|error")
+	bannerUpdateCmd.Flags().StringVar(&bannerTitle, "title", "", "new title")
+	bannerUpdateCmd.Flags().StringVar(&bannerBody, "body", "", "new body")
+	bannerUpdateCmd.Flags().StringVar(&bannerLevel, "level", "", "info|success|warning|error")
+	bannerUpdateCmd.Flags().BoolVar(&bannerActive, "active", true, "set banner active/inactive")
+	BannersCmd.AddCommand(bannerListCmd, bannerCreateCmd, bannerUpdateCmd, bannerDeleteCmd)
+}