feat: add folder filtering and improve list view performance

- Added server-side folder filtering to paginated metadata endpoint with support for regular folders and .trash
- Improved list view performance by optimizing kind filtering and non-markdown file handling
- Updated folder navigation to properly reset other filters (tags, quick links, search) when selecting a folder
- Added request ID tracking to prevent stale responses from affecting pagination state
- Enhanced list view to show loading

server/index-phase3-patch.mjs

@@ -733,9 +733,25 @@ export function setupPaginatedMetadataEndpoint(app, metadataCache, performanceMo
         }
       );
 
-      // Paginate the cached result
-      const paginatedItems = allMetadata.slice(cursor, cursor + limit);
-      const hasMore = cursor + limit < allMetadata.length;
+      // Optional server-side filtering by folder before paginating
+      let filtered = allMetadata;
+      const rawFolder = typeof req.query.folder === 'string' ? req.query.folder : '';
+      const folder = String(rawFolder || '').toLowerCase().replace(/\\/g, '/').replace(/^\/+|\/+$/g, '');
+      if (folder) {
+        filtered = allMetadata.filter(it => {
+          const fp = String(it.filePath || '').toLowerCase().replace(/\\/g, '/');
+          if (!fp) return false;
+          if (folder === '.trash') {
+            return fp.startsWith('.trash/') || fp.includes('/.trash/');
+          }
+          const op = fp.replace(/^\/+|\/+$/g, '');
+          return op === folder || op.startsWith(folder + '/');
+        });
+      }
+
+      // Paginate the filtered result
+      const paginatedItems = filtered.slice(cursor, cursor + limit);
+      const hasMore = cursor + limit < filtered.length;
       const nextCursor = hasMore ? cursor + limit : null;
 
       performanceMonitor.markCache(hit);
@@ -747,7 +763,7 @@ export function setupPaginatedMetadataEndpoint(app, metadataCache, performanceMo
         items: paginatedItems,
         nextCursor,
         hasMore,
-        total: allMetadata.length,
+        total: filtered.length,
         cached: hit,
         duration
       });