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/homework.html

@@ -15,7 +15,7 @@
       font-family: 'Unbounded', sans-serif; font-size: 1.1rem; font-weight: 800;
       color: #0F172A; margin-bottom: 6px;
     }
-    .page-sub { font-size: 0.82rem; color: #8898AA; margin-bottom: 24px; }
+    .page-sub { font-size: 0.82rem; color: var(--text-3); margin-bottom: 24px; }
 
     /* ── top bar with class selector ── */
     .hw-top { display: flex; align-items: center; gap: 14px; margin-bottom: 24px; flex-wrap: wrap; }
@@ -28,7 +28,7 @@
     .hw-sf-btn {
       padding: 6px 14px; border-radius: 999px; border: 1.5px solid rgba(15,23,42,0.1);
       background: transparent; font-family: 'Manrope', sans-serif; font-size: 0.75rem;
-      font-weight: 600; color: #8898AA; cursor: pointer; transition: all .15s;
+      font-weight: 600; color: var(--text-3); cursor: pointer; transition: all .15s;
     }
     .hw-sf-btn:hover { border-color: var(--violet); color: var(--violet); }
     .hw-sf-btn.active { background: rgba(155,93,229,0.08); border-color: var(--violet); color: var(--violet); }
@@ -48,7 +48,7 @@
     }
     .hw-card-body { flex: 1; min-width: 0; }
     .hw-card-title { font-size: 0.88rem; font-weight: 700; color: #0F172A; margin-bottom: 4px; }
-    .hw-card-meta { font-size: 0.75rem; color: #8898AA; display: flex; gap: 12px; flex-wrap: wrap; margin-bottom: 6px; }
+    .hw-card-meta { font-size: 0.75rem; color: var(--text-3); display: flex; gap: 12px; flex-wrap: wrap; margin-bottom: 6px; }
     .hw-card-note { font-size: 0.78rem; color: #3D4F6B; background: rgba(15,23,42,0.03); padding: 8px 12px; border-radius: 10px; margin-top: 8px; line-height: 1.5; }
     .hw-card-note strong { color: #0F172A; }
     .hw-card-actions { display: flex; gap: 8px; margin-top: 10px; flex-wrap: wrap; }
@@ -99,9 +99,9 @@
     .hw-upload-area:hover, .hw-upload-area.dragover {
       border-color: var(--violet); background: rgba(155,93,229,0.02);
     }
-    .hw-upload-icon { color: #8898AA; margin-bottom: 8px; }
+    .hw-upload-icon { color: var(--text-3); margin-bottom: 8px; }
     .hw-upload-text { font-size: 0.85rem; font-weight: 600; color: #3D4F6B; margin-bottom: 4px; }
-    .hw-upload-hint { font-size: 0.72rem; color: #8898AA; }
+    .hw-upload-hint { font-size: 0.72rem; color: var(--text-3); }
 
     /* review modal (inline) */
     .hw-review-panel {
@@ -118,7 +118,7 @@
     .hw-review-panel textarea { min-height: 60px; resize: vertical; }
 
     /* empty state */
-    .hw-empty { text-align: center; padding: 60px 20px; color: #8898AA; }
+    .hw-empty { text-align: center; padding: 60px 20px; color: var(--text-3); }
     .hw-empty-icon { font-size: 3rem; margin-bottom: 12px; opacity: 0.3; }
     .hw-empty-text { font-size: 0.88rem; font-weight: 600; }
 
@@ -164,13 +164,13 @@
                accept=".pdf,.doc,.docx,.ppt,.pptx,.xls,.xlsx,.png,.jpg,.jpeg,.gif,.webp,.txt" />
         <div style="display:flex;gap:10px;margin-bottom:24px;flex-wrap:wrap;align-items:flex-end">
           <div style="flex:1;min-width:200px">
-            <label style="font-size:.72rem;font-weight:700;color:#8898AA;display:block;margin-bottom:4px">Задание (необязательно)</label>
+            <label style="font-size:.72rem;font-weight:700;color:var(--text-3);display:block;margin-bottom:4px">Задание (необязательно)</label>
             <select id="hw-assignment-sel" class="hw-class-sel" style="width:100%">
               <option value="">— Без привязки к заданию —</option>
             </select>
           </div>
           <div style="flex:1;min-width:200px">
-            <label style="font-size:.72rem;font-weight:700;color:#8898AA;display:block;margin-bottom:4px">Комментарий</label>
+            <label style="font-size:.72rem;font-weight:700;color:var(--text-3);display:block;margin-bottom:4px">Комментарий</label>
             <input type="text" id="hw-message" class="hw-class-sel" style="width:100%" placeholder="Опишите работу…" />
           </div>
           <button class="hw-btn hw-btn-primary" id="hw-submit-btn" onclick="submitHomework()" disabled>