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/App/Module/ModuleManifest.php

@@ -72,9 +72,6 @@ final class ModuleManifest
     /** @var list<class-string> AuthorizationPolicyInterface FQCNs */
     public readonly array $authorizationPolicies;
 
-    /** @var array<string, string> UI-capability-key → ability-string for layout authorization */
-    public readonly array $layoutCapabilities;
-
     public readonly ?string $migrationsPath;
 
     public readonly string $basePath;
@@ -109,7 +106,6 @@ final class ModuleManifest
         $this->sessionProviders = self::listOf($raw, 'session_providers');
         $this->permissions = self::normalizePermissions($raw['permissions'] ?? [], $this->id);
         $this->authorizationPolicies = self::listOf($raw, 'authorization_policies');
-        $this->layoutCapabilities = is_array($raw['layout_capabilities'] ?? null) ? $raw['layout_capabilities'] : [];
 
         $migrationsPath = $raw['migrations_path'] ?? null;
         $this->migrationsPath = is_string($migrationsPath) && trim($migrationsPath) !== ''