feat(notifications): ntfy/Gotify push channels with live delivery (#69)

Per-user notification_channels (ntfy + Gotify): every
insertUserNotification now fans out best-effort to enabled channels —
deployment/backup/security/agent alerts reach the user's phone via the
ntfy app with zero extra infrastructure.

- POST/GET/DELETE /notifications/channels + POST .../:id/test which
  pushes a real probe so misconfiguration surfaces before alerts depend
  on it (502 DELIVERY_FAILED on endpoint errors).
- ntfy: POST to endpoint (topic in path), Title/Tags headers, optional
  Bearer token. Gotify: POST {endpoint}/message?token=...
- Delivery is best-effort by design — a dead relay never breaks the
  producing flow; one shared 5s-timeout client.
- CLI `notifications channels list|add|test|remove`, MCP tools,
  OpenAPI paths + NotificationChannel schema.
- Web settings "Push notifications" section and a Push channels card on
  the mobile notifications tab (add/test/remove).

Verified live: channel CRUD, test-ping hit a recording endpoint with
correct headers/body, and a real deployment fanned out "Deployment
succeeded" through the channel end-to-end.

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

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

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

@@ -1,6 +1,8 @@
 package commands
 
 import (
+	"fmt"
+
 	"github.com/spf13/cobra"
 )
 
@@ -60,6 +62,104 @@ var notifReadCmd = &cobra.Command{
 	},
 }
 
+var notifChannelsCmd = &cobra.Command{
+	Use:   "channels",
+	Short: "Manage push notification channels (ntfy/Gotify)",
+}
+
+var notifChannelsListCmd = &cobra.Command{
+	Use:   "list",
+	Short: "List push channels",
+	RunE: func(cmd *cobra.Command, args []string) error {
+		c, err := client()
+		if err != nil {
+			return err
+		}
+		data, err := c.Do("GET", "/notifications/channels", nil)
+		if err != nil {
+			return err
+		}
+		items, err := unwrapList(data, "channels")
+		if err != nil {
+			return err
+		}
+		rows := make([][]string, 0, len(items))
+		for _, n := range items {
+			rows = append(rows, []string{
+				str(n, "id"), str(n, "kind"), str(n, "endpoint"), str(n, "enabled"), relTime(n, "created_at"),
+			})
+		}
+		printRows(data, []string{"ID", "KIND", "ENDPOINT", "ENABLED", "AGE"}, rows)
+		return nil
+	},
+}
+
+var notifChannelsAddCmd = &cobra.Command{
+	Use:   "add <ntfy|gotify> <endpoint>",
+	Short: "Add a push channel (endpoint includes topic for ntfy)",
+	Args:  cobra.ExactArgs(2),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		c, err := client()
+		if err != nil {
+			return err
+		}
+		token, _ := cmd.Flags().GetString("token")
+		data, err := c.Do("POST", "/notifications/channels", map[string]interface{}{
+			"kind":     args[0],
+			"endpoint": args[1],
+			"token":    token,
+		})
+		if err != nil {
+			return err
+		}
+		PrintRaw(data)
+		return nil
+	},
+}
+
+var notifChannelsTestCmd = &cobra.Command{
+	Use:   "test <id>",
+	Short: "Send a test notification through a channel",
+	Args:  cobra.ExactArgs(1),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		c, err := client()
+		if err != nil {
+			return err
+		}
+		data, err := c.Do("POST", "/notifications/channels/"+args[0]+"/test", map[string]interface{}{})
+		if err != nil {
+			return err
+		}
+		PrintRaw(data)
+		return nil
+	},
+}
+
+var notifChannelsRemoveCmd = &cobra.Command{
+	Use:   "remove <id>",
+	Short: "Remove a push channel",
+	Args:  cobra.ExactArgs(1),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		yes, _ := cmd.Flags().GetBool("yes")
+		if !yes && !Confirm(fmt.Sprintf("Remove channel %s?", args[0])) {
+			return nil
+		}
+		c, err := client()
+		if err != nil {
+			return err
+		}
+		data, err := c.Do("DELETE", "/notifications/channels/"+args[0], nil)
+		if err != nil {
+			return err
+		}
+		PrintRaw(data)
+		return nil
+	},
+}
+
 func init() {
-	NotificationsCmd.AddCommand(notifListCmd, notifReadCmd)
+	notifChannelsAddCmd.Flags().String("token", "", "Auth token (ntfy access token or Gotify app token)")
+	notifChannelsRemoveCmd.Flags().Bool("yes", false, "Skip confirmation")
+	notifChannelsCmd.AddCommand(notifChannelsListCmd, notifChannelsAddCmd, notifChannelsTestCmd, notifChannelsRemoveCmd)
+	NotificationsCmd.AddCommand(notifListCmd, notifReadCmd, notifChannelsCmd)
 }