a11y: WCAG AA contrast + ARIA roles + focus management across all pages

- css/ls.css: --text-3 #8898AA → #56687A (5.1:1 contrast), min-height 44px on .btn-primary/.btn-ghost/.sb-link, new .icon-btn utility (44×44px)
- js/api.js: lsConfirm — role=dialog, aria-modal, aria-labelledby, Tab focus trap, restore focus on close; lsToast — aria-live=polite on container, role=alert on errors; live quiz — role=dialog, role=radiogroup, role=radio, aria-checked, keyboard support
- test-run.html: q-opt divs — role=radio/checkbox, aria-checked, tabindex, keyboard enter/space; confirm modal — role=dialog, aria-modal; btn-flag — aria-pressed; dots — aria-label, aria-current; touch targets 44px
- board.html: btn-del-ann — aria-label; reaction buttons — aria-label, aria-pressed
- All 18 HTML files: replace hardcoded color:#8898AA with color:var(--text-3)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/lab.html

@@ -9213,7 +9213,7 @@
         const p = permData.permissions?.find(p => p.key === 'simulations.access');
         if (p && p.effective === false) {
           document.getElementById('sim-grid').innerHTML =
-            `<div style="grid-column:1/-1;padding:60px 0;text-align:center;color:#8898AA">
+            `<div style="grid-column:1/-1;padding:60px 0;text-align:center;color:var(--text-3)">
               <div style="font-size:2rem;margin-bottom:12px"><svg class="ic" viewBox="0 0 24 24"><rect x="3" y="11" width="18" height="11" rx="2" ry="2"/><path d="M7 11V7a5 5 0 0 1 10 0v4"/></svg></div>
               <div style="font-family:'Unbounded',sans-serif;font-size:1rem;font-weight:800;color:#0F172A;margin-bottom:6px">Доступ к симуляциям закрыт</div>
               <div style="font-size:.88rem">Администратор ограничил доступ к лаборатории</div>
@@ -9229,7 +9229,7 @@
 
       if (_simModuleDisabled) {
         document.getElementById('sim-grid').innerHTML =
-          `<div style="grid-column:1/-1;padding:60px 0;text-align:center;color:#8898AA">
+          `<div style="grid-column:1/-1;padding:60px 0;text-align:center;color:var(--text-3)">
             <div style="font-size:2rem;margin-bottom:12px"><svg class="ic" viewBox="0 0 24 24"><rect x="3" y="11" width="18" height="11" rx="2" ry="2"/><path d="M7 11V7a5 5 0 0 1 10 0v4"/></svg></div>
             <div style="font-family:'Unbounded',sans-serif;font-size:1rem;font-weight:800;color:#0F172A;margin-bottom:6px">Модуль симуляций отключён</div>
             <div style="font-size:.88rem">Администратор временно отключил лабораторию</div>