ci: publish templates to the control panel on main

Adds `gbrgames export`, which builds the games_published payload from
every game.yaml, and a CI step that posts it to the panel webhook after
validation on main. Unlike the node-agent notify, a failed publish fails
the run so stale templates in the panel never go unnoticed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmd/gbrgames/main.go

@@ -2,6 +2,7 @@
 //
 //	go run ./cmd/gbrgames validate            # check every games/<id>/game.yaml (+ test.yaml)
 //	go run ./cmd/gbrgames import export.json  # write games/<id>/ from GET /api/v1/admin/games
+//	go run ./cmd/gbrgames export -out p.json  # build the games_published payload CI sends to the panel
 package main
 
 import (
@@ -19,6 +20,8 @@ func main() {
 		err = runValidate(os.Args[2:])
 	case "import":
 		err = runImport(os.Args[2:])
+	case "export":
+		err = runExport(os.Args[2:])
 	default:
 		usage()
 	}
@@ -29,6 +32,6 @@ func main() {
 }
 
 func usage() {
-	fmt.Fprintln(os.Stderr, "usage: gbrgames validate [-games DIR] | import [-games DIR] [-all] EXPORT.json")
+	fmt.Fprintln(os.Stderr, "usage: gbrgames validate [-games DIR] | import [-games DIR] [-all] EXPORT.json | export [-repo R] [-commit SHA] [-out FILE]")
 	os.Exit(2)
 }