feat: implement full breadcrumb path navigation in Files tab

- Add breadcrumbPath array to app state for tracking folder hierarchy
- Rewrite updateBreadcrumb() to render full path: Home > folder > subfolder
- Each breadcrumb segment is clickable to navigate back to that level
- Current folder shown in bold (non-clickable), parent folders as links
- Reset breadcrumb path on tab switch, home navigation, and initial load
- Update navigateFolder/selectFolder to push to breadcrumb path
- Enhanced breadcrumb CSS with hover effects and dark mode support

static/js/app/navigation.js

@@ -76,7 +76,8 @@ function switchToFilesView() {
 
     if (window.app.userHomeFolderId) {
         window.app.currentPath = window.app.userHomeFolderId;
-        window.ui.updateBreadcrumb(window.app.userHomeFolderName || 'Home');
+        window.app.breadcrumbPath = [];
+        window.ui.updateBreadcrumb();
     } else {
         window.app.currentPath = '';
     }