feat(build): mark scaffolded files with //summer:make and pass the app to generated commands (quick-261028-pq8)

- model, migration, command, job and admin-controller stubs start with
  //summer:make <kind>; registry.gen.go keeps its generated-code header
- the registry scan accepts the directive and the older header
- command functions may take one *backpack.App; generatedCommands takes a
  variadic app, so plugin.go files calling generatedCommands() still compile
- scaffolded plugins keep the app from Boot and return generatedCommands(p.app)
- make:command notes the nil app for an older plugin.go
- docs, help text and the blog example follow

docs/examples/blog/plugin.go

@@ -72,10 +72,11 @@ func (p *Plugin) AdminControllers() []pact.AdminController {
 	return generatedAdminControllers()
 }
 
-// Commands returns the generated commands plus blog:publish, which needs the
-// database and so is built here with the plugin's withDB.
+// Commands returns the generated commands, which receive the application
+// kept in Boot, plus blog:publish. That one takes the narrower withDB, which
+// its tests replace, so it is added here by hand.
 func (p *Plugin) Commands() []bonfire.Command {
-	return append(generatedCommands(), console.PublishCommand(p.withDB))
+	return append(generatedCommands(p.app), console.PublishCommand(p.withDB))
 }
 
 // AdminFS is the admin YAML the controllers read: controllers/posts and