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/registerContainer.php

@@ -44,8 +44,9 @@ $moduleRegistry = ModuleRegistry::boot($modulesDir, $enabledModules);
 
 $container->set(ModuleRegistry::class, static fn (): ModuleRegistry => $moduleRegistry);
 
-$coreKeys = []; // snapshot keys before module registrars
-// We use reflection-free approach: track what the container had before modules
+// Disallow overriding existing core bindings from module registrars.
+$container->protectExistingBindings();
+
 foreach ($moduleRegistry->getContainerRegistrars() as $registrarClass) {
     if (!class_exists($registrarClass)) {
         throw new RuntimeException("Module container registrar class not found: {$registrarClass}");