Add focus-visible outline for buttons; enrich search input a11y hints

- Provide :focus-visible outline for .normal-button to improve keyboard
  navigation visibility
- Add aria-keyshortcuts and spellCheck=false to search input
Build and lint pass.

Author: PeterDaveHello

src/pages/IndependentPanel/App.jsx

@@ -227,6 +227,8 @@ function App() {
               aria-label={t('Search')}
               aria-controls="chat-list"
               enterKeyHint="search"
+              aria-keyshortcuts="/ Control+F Meta+F"
+              spellCheck={false}
               autoComplete="off"
               ref={searchInputRef}
             />

src/pages/IndependentPanel/styles.scss

@@ -179,6 +179,11 @@
     overflow: hidden;
   }
 
+  .normal-button:focus-visible {
+    outline: 2px solid var(--font-active-color);
+    outline-offset: 2px;
+  }
+
   .gpt-util-group {
     display: flex;
     gap: 15px;