Harden: Fix critical accessibility issues

- Add aria-labels to icon-only buttons (refresh, language toggle)
- Add aria-hidden to decorative SVGs
- Add aria-label to data source select
- Replace outline:none with visible focus rings on all inputs/selects
- Add <main> landmark for screen reader navigation
- Add prefers-reduced-motion: disable all animations for vestibular safety
- Move error message inline style to CSS class
- Add aria-label to both nav landmarks

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

src/App.css

@@ -84,6 +84,17 @@ html[dir="rtl"] {
   background: var(--text-secondary);
 }
 
+.error-container button:focus-visible {
+  outline: 2px solid var(--accent);
+  outline-offset: 2px;
+}
+
+.error-message {
+  max-width: 400px;
+  text-align: center;
+  color: var(--text-muted);
+}
+
 /* Empty State */
 .empty-state {
   display: flex;
@@ -216,7 +227,8 @@ html[dir="rtl"] {
 }
 
 .data-source-select:focus {
-  outline: none;
+  outline: 2px solid var(--accent);
+  outline-offset: 1px;
   background-color: rgba(59, 130, 246, 0.12);
 }
 
@@ -673,7 +685,8 @@ table tbody tr:hover {
 
 .control-group select:focus,
 .control-group input[type="date"]:focus {
-  outline: none;
+  outline: 2px solid var(--accent);
+  outline-offset: -1px;
   border-color: var(--accent);
 }
 
@@ -1679,7 +1692,8 @@ table tbody tr:hover {
 
 .editor-section input:focus,
 .editor-section select:focus {
-  outline: none;
+  outline: 2px solid var(--accent);
+  outline-offset: -1px;
   border-color: var(--accent);
 }
 
@@ -1988,6 +2002,21 @@ html[dir="rtl"] .chart-export-btn.visible {
   text-align: left !important;
 }
 
+/* ========================================
+   Reduced Motion
+   ======================================== */
+
+@media (prefers-reduced-motion: reduce) {
+  *, *::before, *::after {
+    animation-duration: 0.01ms !important;
+    animation-iteration-count: 1 !important;
+    transition-duration: 0.01ms !important;
+  }
+  .carousel-track {
+    transition: none;
+  }
+}
+
 /* ========================================
    Loading Skeleton
    ======================================== */