refactor: simplify module platform — drop custom autoloader, layout_capabilities indirection, and absolute template paths

- Replace ModuleAutoloader with Composer ClassLoader (addPsr4 via spl_autoload_functions)
- Eliminate layout_capabilities mapping; UI slots reference ability strings directly
- Resolve relative template paths in ModuleRegistry instead of baking __DIR__ into manifests

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/Service/Access/UiCapabilityMap.php

@@ -7,8 +7,8 @@ final class UiCapabilityMap
     /**
      * Core layout capabilities — admin panel visibility checks.
      *
-     * Module-contributed capabilities are registered via the module manifest's
-     * 'layout_capabilities' field and merged dynamically in UiAccessService.
+     * Module abilities are collected from UI slot 'permission' fields and
+     * merged dynamically in UiAccessService::layoutCapabilities().
      *
      * @var array<string, string>
      */