feat: extend module platform with UI slots, runtime components, CLI tooling and {{userId}} search support

Completes the generic module platform that enables modules to contribute
UI elements, runtime JS components, and search resources without any
core hardcoding.

New generic UI slot types:
- topbar.right_item: module-contributed topbar buttons
- layout.body_end_template: module-contributed dialog/overlay templates
- layout.head_style: module-contributed global CSS
- runtime.component: declarative JS component registration with phase ordering

New infrastructure:
- ModuleAutoloader: PSR-4 autoloading for module-local PHP classes
- ModuleRuntimePageBuilder: symlinks module pages into runtime directory
- ModuleRuntimeAssetPublisher: publishes module CSS/JS to web/modules/
- ModulePermissionSynchronizer: syncs module permissions to DB
- CLI scripts: module-runtime-sync, module-build, module-migrate,
  module-permissions-sync, module-assets-sync
- {{userId}} placeholder in SearchDataService for user-scoped search queries
- Component runtime with phased initialization (early/default/late)
- AppContainer.protectExistingBindings() to prevent module→core overwrites
- Architecture tests: ModuleStructureContractTest, CoreTemplateIsolationTest,
  FrontendComponentRuntimeContractTest, AppContainerIsolationContractTest

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

lib/App/Module/ModuleAutoloader.php

@@ -0,0 +1,56 @@
+<?php
+
+namespace MintyPHP\App\Module;
+
+/**
+ * Runtime autoloader for module-local PHP classes.
+ *
+ * Modules can place PHP code under modules/<id>/lib and use the same
+ * MintyPHP namespace root as core classes.
+ */
+final class ModuleAutoloader
+{
+    /** @var list<string> */
+    private static array $moduleLibDirs = [];
+
+    private static bool $registered = false;
+
+    /**
+     * @param list<ModuleManifest> $manifests
+     */
+    public static function register(array $manifests): void
+    {
+        $dirs = self::$moduleLibDirs;
+        foreach ($manifests as $manifest) {
+            $libDir = rtrim($manifest->basePath, '/') . '/lib';
+            if (is_dir($libDir)) {
+                $dirs[] = $libDir;
+            }
+        }
+        self::$moduleLibDirs = array_values(array_unique($dirs));
+
+        if (self::$registered) {
+            return;
+        }
+
+        spl_autoload_register([self::class, 'autoload'], true, true);
+        self::$registered = true;
+    }
+
+    private static function autoload(string $class): void
+    {
+        $prefix = 'MintyPHP\\';
+        if (!str_starts_with($class, $prefix)) {
+            return;
+        }
+
+        $relativePath = str_replace('\\', '/', substr($class, strlen($prefix))) . '.php';
+        foreach (self::$moduleLibDirs as $libDir) {
+            $candidate = $libDir . '/' . $relativePath;
+            if (is_file($candidate)) {
+                require_once $candidate;
+                return;
+            }
+        }
+    }
+}