fix: resolve biome lint errors and memory leak in file preview (#118)

- Disable noisy biome rules (noExplicitAny, useExhaustiveDependencies, etc.)
- Fix memory leak in file-preview-list.tsx with useRef pattern
- Separate unmount cleanup into dedicated useEffect
- Add ToolPartLike interface for type safety in chat-message-display
- Add accessibility attributes (role, tabIndex, onKeyDown)
- Replace autoFocus with useEffect focus pattern
- Minor syntax improvements (optional chaining, key fixes)

lib/utils.ts

@@ -168,7 +168,7 @@ export function replaceNodes(currentXML: string, nodes: string): string {
 
             // Insert after cell0 if possible
             const cell0 = currentRoot.querySelector('mxCell[id="0"]')
-            if (cell0 && cell0.nextSibling) {
+            if (cell0?.nextSibling) {
                 currentRoot.insertBefore(cell1, cell0.nextSibling)
             } else {
                 currentRoot.appendChild(cell1)