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>

web/js/components/app-multiselect-cascade.js

@@ -2,7 +2,7 @@
  * Cascading multi-select — filters child options based on parent selection.
  */
 import { getMultiSelectInstance } from './app-multiselect-init.js';
-import { warnOnce } from '../core/app-dom.js';
+import { warnOnce, resolveHost } from '../core/app-dom.js';
 
 const parseValueList = (value) =>
   String(value || '')
@@ -15,19 +15,6 @@ const setDisabledState = (option, disabled) => {
   option.classList.toggle('is-disabled', disabled);
   option.setAttribute('aria-disabled', disabled ? 'true' : 'false');
   option.style.pointerEvents = disabled ? 'none' : '';
-  if (!option._cascadeGuard) {
-    option.addEventListener(
-      'click',
-      (event) => {
-        if (option.dataset.disabled === '1') {
-          event.preventDefault();
-          event.stopImmediatePropagation();
-        }
-      },
-      true
-    );
-    option._cascadeGuard = true;
-  }
 };
 
 const toggleSelectAll = (instance, disabled) => {
@@ -44,9 +31,11 @@ export const initMultiSelectCascade = ({
   map = {},
   mode = 'disable',
   clearInvalid = true,
-}) => {
-  const parentInput = typeof parent === 'string' ? document.querySelector(parent) : parent;
-  const childInput = typeof child === 'string' ? document.querySelector(child) : child;
+  root = document,
+} = {}) => {
+  const host = resolveHost(root);
+  const parentInput = typeof parent === 'string' ? host.querySelector(parent) : parent;
+  const childInput = typeof child === 'string' ? host.querySelector(child) : child;
   if (!parentInput || !childInput) {
     if (!parentInput) {
       warnOnce('UI_EL_MISSING', `Missing multiselect parent: ${parent}`, { module: 'multiselect-cascade' });
@@ -54,13 +43,13 @@ export const initMultiSelectCascade = ({
     if (!childInput) {
       warnOnce('UI_EL_MISSING', `Missing multiselect child: ${child}`, { module: 'multiselect-cascade' });
     }
-    return;
+    return { destroy: () => {} };
   }
 
-  const childInstance = getMultiSelectInstance(childInput);
+  const childInstance = getMultiSelectInstance(childInput, host);
   if (!childInstance) {
     warnOnce('UI_INIT_MISSING', 'Missing multiselect instance for child', { module: 'multiselect-cascade' });
-    return;
+    return { destroy: () => {} };
   }
 
   const apply = () => {
@@ -98,4 +87,13 @@ export const initMultiSelectCascade = ({
 
   parentInput.addEventListener('change', apply);
   apply();
+
+  return {
+    destroy: () => {
+      parentInput.removeEventListener('change', apply);
+      const options = childInstance.element.querySelectorAll('.multi-select-option');
+      options.forEach((option) => setDisabledState(option, false));
+      toggleSelectAll(childInstance, false);
+    },
+  };
 };