refactor: extract shared form utils, add aria-live regions and reduced-motion support

DRY duplicated helpers (escapeAttr, belongsToForm, isSubmitControl,
isEditableTarget) into web/js/core/app-form-utils.js and update 7
consumers. Add aria-live="polite" to flash messages, async messages,
and search results for screen reader announcements. Add
prefers-reduced-motion support to CSS tooltips.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/js/components/app-toggle-aside-panels.js

@@ -2,6 +2,7 @@
  * Aside panel switcher — opens/closes named sidebar panels.
  */
 import { requireEl, warnOnce } from '../core/app-dom.js';
+import { isEditableTarget } from '../core/app-form-utils.js';
 import { initPersistedDetailsGroup } from '../core/app-details-open-state.js';
 
 export function initAsidePanels(options = {}) {
@@ -40,12 +41,6 @@ export function initAsidePanels(options = {}) {
   const getTabKey = (tab) => tab?.dataset?.asideTarget || '';
   const getPanelTools = (panel) => panel?.querySelector('[data-aside-panel-tools]') || null;
   const getTabHref = (tab) => tab?.dataset?.asideHref || '';
-  const isEditableTarget = (target) => {
-    if (!target) {return false;}
-    if (target.isContentEditable) {return true;}
-    const tag = target.tagName;
-    return tag === 'INPUT' || tag === 'TEXTAREA' || tag === 'SELECT';
-  };
 
   const panelDetailsRegistry = new WeakMap();
   const findActiveDetailsKeys = (panel) => Array.from(panel.querySelectorAll('details[data-details-key]'))