fix: resolve event-listener leaks and CSS gaps found in code quality audit

- notes.js (Critical): move grid click listener from renderGrid() to
  render() — was re-registered on every save/pin/delete, causing
  multiple API calls per user action after several interactions
- dashboard.js (Major): introduce AbortController (_fabController) so
  the anonymous document click listener from initFab() is cancelled on
  each new render() cycle; also remove the redundant initFab() call on
  the skeleton render
- layout.css (Major): extend .label selector to include .form-label,
  covering usage in notes.js and settings.js without a mass-rename
- test-modal-utils.js (Major): 12 unit tests for wireBlurValidation,
  btnSuccess, btnError; registered as test:modal-utils in package.json
- notes.js (Minor): add btnError() shake feedback to save error handler
- calendar.js (Minor): add popup.isConnected guard to closePopup so
  the listener self-removes correctly after navigation without a click

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

public/pages/dashboard.js

@@ -6,6 +6,9 @@
 
 import { api } from '/api.js';
 
+// Hält den AbortController des aktuellen FAB-Listeners — wird bei jedem render() erneuert.
+let _fabController = null;
+
 // --------------------------------------------------------
 // Hilfsfunktionen
 // --------------------------------------------------------
@@ -339,7 +342,7 @@ function renderFab() {
   `;
 }
 
-function initFab(container) {
+function initFab(container, signal) {
   const fabMain    = container.querySelector('#fab-main');
   const fabActions = container.querySelector('#fab-actions');
   if (!fabMain) return;
@@ -368,7 +371,7 @@ function initFab(container) {
     });
   });
 
-  document.addEventListener('click', () => { if (open) toggleFab(false); });
+  document.addEventListener('click', () => { if (open) toggleFab(false); }, { signal });
 }
 
 // --------------------------------------------------------
@@ -395,6 +398,9 @@ function wireLinks(container) {
 // --------------------------------------------------------
 
 export async function render(container, { user }) {
+  _fabController?.abort();
+  _fabController = new AbortController();
+
   container.innerHTML = `
     <div class="dashboard">
       <div class="dashboard__grid">
@@ -412,7 +418,6 @@ export async function render(container, { user }) {
     </div>
     ${renderFab()}
   `;
-  initFab(container);
 
   let data    = { upcomingEvents: [], urgentTasks: [], todayMeals: [], pinnedNotes: [] };
   let weather = null;
@@ -455,6 +460,6 @@ export async function render(container, { user }) {
   `;
 
   wireLinks(container);
-  initFab(container);
+  initFab(container, _fabController.signal);
   if (window.lucide) window.lucide.createIcons();
 }