Document single action controllers

[filipebraida]

The v6 docs covered single action controllers, but the section was not carried over to v7. This adds it back to the controllers guide, adapted to the v7 barrel file syntax.

What is covered

• The handle method convention, with a complete controller example.
• Binding the controller to a route by passing it in an array with no method name.
• The auto-generated route name.
• A dependency injection example, since single action controllers are ordinary controllers.
• A note on naming them after the operation rather than a resource.

Beyond the v6 content

Two details that were not in the v6 docs:

Scaffolding the controller. make:controller accepts action names as positional arguments, so node ace make:controller register_newsletter_subscription handle --singular generates the class with handle already in place via actions.stub.

The --singular flag is required here. Without it, generators.controllerName() calls .plural() and produces RegisterNewsletterSubscriptionsController, which defeats the purpose of a single action controller. This felt worth calling out explicitly rather than leaving as a surprise.

Placement

The section sits between "Dependency injection" and "Resource-driven controllers", so the two controller design patterns read as a pair. The guide's intro bullet list was updated to match.

Verification

• Behaviour checked against @adonisjs/http-server@9.2.0, where the array form resolves handler[1] ?? 'handle', and the route name is the snake_cased controller name with no .handle segment appended.
• Generator behaviour checked against @adonisjs/core@7.4.0 (commands/make/controller.js, make/controller/actions.stub) and @adonisjs/application@9.0.1 (controllerName/controllerFileName).
• Rendered locally with node ace serve --hmr: the [!code ++] markers highlight the four intended lines, the tip callout renders, and the #makecontroller cross-reference resolves to an existing anchor.
• prettier --check and npm run lint pass.