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/state.js

@@ -19,7 +19,8 @@ window.app = {
     isSearchMode: false,
     shareDialogItem: null,
     shareDialogItemType: null,
-    notificationShareUrl: null
+    notificationShareUrl: null,
+    breadcrumbPath: [] // Array of {id, name} tracking folder navigation hierarchy
 };
 
 window.appElements = {