Add local file open support and improve URL handling

Introduces a dialog to open local HTML files via Ctrl+O/Cmd+O, converting file paths to file:// URLs for navigation. Also improves input handling by stripping quotes and better detecting local file paths. Updates bookmarks and clears site history.

preload.js

@@ -55,6 +55,14 @@ const electronAPI = {
       console.error('IPC open-devtools error:', err);
       return Promise.reject(err);
     }
+  },
+  openLocalFile: async () => {
+    try {
+      return await ipcRenderer.invoke('show-open-file-dialog');
+    } catch (err) {
+      console.error('IPC openLocalFile error:', err);
+      return null;
+    }
   }
 };