Introduce typed DTOs and sub-namespaces for Micropub handlers

Each handler now declares the data class it needs via dataClass(). The
controller builds the appropriate typed DTO from the raw request array
before calling handle(), giving handlers typed property access instead
of raw array lookups.

Handlers moved to App\Services\Micropub\Handlers, data objects to
App\Services\Micropub\Data. MicropubHandlerRegistry and the interface
are documented with flow diagrams and guidance for adding new types.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Services/Micropub/MicropubHandlerRegistry.php

@@ -5,7 +5,27 @@ declare(strict_types=1);
 namespace App\Services\Micropub;
 
 use App\Exceptions\MicropubHandlerException;
+use App\Services\Micropub\Handlers\MicropubHandlerInterface;
 
+/**
+ * Maps Micropub post types to their handler instances.
+ *
+ * MicropubRequest normalises every incoming request and resolves it to a type
+ * string ("entry", "card", "update"). The controller asks the registry for the
+ * right handler, then asks the handler which data class to build, and finally
+ * calls handle() with that data object.
+ *
+ * Flow:
+ *   MicropubRequest (normalise) → MicropubController
+ *     → MicropubHandlerRegistry::getHandler($type)
+ *     → $handler->dataClass()::fromArray($rawData)
+ *     → $handler->handle($dataObject)
+ *
+ * Handlers are registered in MicropubServiceProvider. To support a new
+ * Micropub post type, create a handler in App\Services\Micropub\Handlers, a
+ * matching data class in App\Services\Micropub\Data, and register the handler
+ * here with its type string.
+ */
 class MicropubHandlerRegistry
 {
     /**
@@ -13,6 +33,9 @@ class MicropubHandlerRegistry
      */
     protected array $handlers = [];
 
+    /**
+     * Register a handler for a given Micropub type string.
+     */
     public function register(string $type, MicropubHandlerInterface $handler): self
     {
         $this->handlers[$type] = $handler;
@@ -21,6 +44,8 @@ class MicropubHandlerRegistry
     }
 
     /**
+     * Retrieve the handler for a given type, or throw if none is registered.
+     *
      * @throws MicropubHandlerException
      */
     public function getHandler(string $type): MicropubHandlerInterface