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>

tests/App/AppContainerTest.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace MintyPHP\Tests\App;
+
+use MintyPHP\App\AppContainer;
+use PHPUnit\Framework\TestCase;
+use RuntimeException;
+
+final class AppContainerTest extends TestCase
+{
+    public function testOverwritingBindingIsAllowedBeforeProtection(): void
+    {
+        $container = new AppContainer();
+        $container->set('service.test', static fn (): string => 'first');
+        $container->set('service.test', static fn (): string => 'second');
+
+        self::assertSame('second', $container->get('service.test'));
+    }
+
+    public function testOverwritingExistingBindingIsBlockedAfterProtection(): void
+    {
+        $container = new AppContainer();
+        $container->set('service.test', static fn (): string => 'first');
+        $container->protectExistingBindings();
+
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage('Refusing to overwrite existing service binding: service.test');
+        $container->set('service.test', static fn (): string => 'second');
+    }
+
+    public function testAddingNewBindingStillWorksAfterProtection(): void
+    {
+        $container = new AppContainer();
+        $container->set('service.first', static fn (): string => 'first');
+        $container->protectExistingBindings();
+        $container->set('service.second', static fn (): string => 'second');
+
+        self::assertSame('second', $container->get('service.second'));
+    }
+}