fix: validate and clamp sidebar width read from localStorage (#152)

* fix: add periodic health polling to prevent stale sidebar status dots

checkConnectionHealth was defined but never called after init().
Add a 30s setInterval useEffect so health status updates automatically
without requiring a page refresh.

Fixes #144

* fix: add aria-labels to Toolbar icon-only buttons for screen reader accessibility

View mode and theme dropdown triggers had aria-haspopup/aria-expanded
but no aria-label — screen readers announced them as generic 'button'.
Decorative SVG icons and color dots inside buttons were also read aloud
causing double-announcement.

Changes:
- Add dynamic aria-label to view mode dropdown trigger
- Add dynamic aria-label to theme dropdown trigger
- Add aria-hidden to decorative icons inside view/theme dropdowns
- Add aria-hidden to ChevronIcon in both dropdown triggers
- Add aria-hidden to color dot divs in theme dropdown items

Fixes #143

* fix: make global search results keyboard navigable

Search result divs had onClick but no role, tabIndex, or onKeyDown.
Keyboard-only users could not Tab to results or activate them.

- Add role=button to each result div
- Add tabIndex=0 to make results focusable via Tab
- Add onKeyDown handler for Enter and Space keys
- Add aria-label announcing table name and match count
- Add cursor:pointer for visual consistency

Fixes #142

* fix: add role=alert to write-mode warning banner for screen readers

Warning banner had no ARIA live region — screen readers silently
ignored it, leaving visually impaired users unaware they were in
a mode allowing destructive database operations.

- Add role=alert to the warning banner div
- Add aria-live=assertive to interrupt and announce immediately
- Add aria-atomic=true to read the full message as one unit
- Add aria-hidden=true to the decorative AlertTriangleIcon

Fixes #141

* fix: validate and clamp sidebar width read from localStorage

parseInt() result was used directly with no validation.
Corrupted values like 'abc' produced NaN causing layout collapse.
Out-of-range values like 9999 caused sidebar to fill entire viewport.

- Parse to int then guard with isNaN() fallback to 240
- Clamp between 180-480px to match drag handler validation logic

Fixes #140

* fix: add 300ms debounce to global search to prevent per-keystroke API calls

Global search fired a fetch on every keystroke with no debounce.
Typing a 5-character word sent 5 separate requests causing unnecessary
backend load and potential race conditions.

- Wrap fetch in setTimeout(300ms)
- Return clearTimeout as cleanup to cancel pending request on each keystroke
- Move setGlobalSearchLoading(true) before timeout for instant UI feedback

Fixes #139

Author: Nakshathra-2808

frontend/src/App.tsx

@@ -162,7 +162,8 @@ export default function App() {
     useState(false);
   const [sidebarWidth, setSidebarWidth] = useState(() => {
     const stored = localStorage.getItem("dbportal-sidebar-width");
-    return stored ? parseInt(stored, 10) : 240;
+    const parsed = stored ? parseInt(stored, 10) : 240;
+    return isNaN(parsed) ? 240 : Math.max(180, Math.min(480, parsed));
   });
 
   const handleSidebarMouseDown = useCallback(