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

cmd/summer/main.go

@@ -207,9 +207,10 @@ func makeCommandCommand() bonfire.Command {
 		Long: `Writes console/<name>.go with a bonfire.Command named <plugin>:<name> in the
 plugin with this ID or the plugin whose directory you are in; the generated
 registry adds it to the commands the plugin returns. The generated function
-takes no arguments, so a command that needs the database or another service
-takes a parameter instead and is returned from the plugin's Commands by hand
-(see the porting guide's blog:publish).`,
+receives the application the plugin kept from Boot (*backpack.App), which
+gives it the config and the services plugins publish. A function with another
+parameter, such as the porting guide's withDB for blog:publish, is returned
+from the plugin's Commands by hand.`,
 		Examples: []bonfire.Example{
 			{Command: "make:command acme.blog Publish", Description: "A blog:publish command in acme.blog"},
 			{Command: "make:command Publish", Description: "The same from inside plugins/acme/blog"},