feat(build): scaffold working admin controllers with model, AdminFS and delete (quick-261028-pq8)

- make:admin-controller edits the singular of its name (--model overrides):
  ModelName, modelClass and the YAML under models/<model>/
- NewRecord returns &models.<Model>{} when the model exists; otherwise the
  nil body stays and the command says to run make:model
- config_list.yaml offers create and delete with showCheckboxes
- registry.gen.go embeds controllers/*/*.yaml and models/*/*.yaml once they
  exist and exposes generatedAdminFS(); scaffolded plugins implement
  pact.AdminAssets through it, and a plugin without AdminFS gets a note
- blog example moves its YAML to models/post; docs and help text follow

docs/backend/admin-controllers.md

@@ -152,9 +152,10 @@ func (p *BlogPlugin) Settings() []pact.SettingsItem {
 
 ```sh
 summer make:admin-controller acme.blog Posts
+summer make:admin-controller acme.blog People --model Person
 ```
 
-The generated controller requires the permission `acme.blog.access_posts`, so declare it in the plugin's `pact.HasPermissions` or the admin API refuses to start with an unknown-permission error. Its `NewRecord` returns `nil` until you return the model, and the list and every write answer 500 until then. The controller ID maps to the admin API path: `acme.blog.posts` is served under `<prefix>/api/v1/acme/blog/posts`. The admin prefix is `backend.uri`, `/backend` by default. A model's `Fillable` method decides which form fields the API may write; see [Forms](forms.md). The admin finds a model's columns through its struct fields, including those of an embedded struct such as `gorm.Model`. A field with a `gorm:"column:..."` tag is known by that column alone; an untagged field is known by GORM's default column name.
+The controller edits the singular of its name, `Post` for `Posts`, unless `--model` names the model: `ModelName` and both `modelClass` values carry it, and `fields.yaml` and `columns.yaml` go under `models/post/`, as in WinterCMS. When the plugin's `models` package already declares the model, `NewRecord` returns it; otherwise `NewRecord` returns `nil` and the list and every write answer 500 until you run `summer make:model` and return the model. The list toolbar offers `create` and `delete`, with `showCheckboxes: true`, which the `delete` button needs. A plugin scaffolded with `summer make:plugin` implements `pact.AdminAssets`: its `AdminFS` returns `generatedAdminFS()`, the controller and model YAML `registry.gen.go` embeds; for a plugin without an `AdminFS` method the command prints a note. The generated controller requires the permission `acme.blog.access_posts`, so declare it in the plugin's `pact.HasPermissions` or the admin API refuses to start with an unknown-permission error. The controller ID maps to the admin API path: `acme.blog.posts` is served under `<prefix>/api/v1/acme/blog/posts`. The admin prefix is `backend.uri`, `/backend` by default. A model's `Fillable` method decides which form fields the API may write; see [Forms](forms.md). The admin finds a model's columns through its struct fields, including those of an embedded struct such as `gorm.Model`. A field with a `gorm:"column:..."` tag is known by that column alone; an untagged field is known by GORM's default column name.
 
 ## Compilation at boot