fix(vfs): add sourceId+verbType optimization to fix readdir()

CRITICAL VFS BUG FIX - Root Cause Analysis:

The issue was that baseStorage.getVerbs() had optimizations for:
- sourceId only
- targetId only
- verbType only

But VFS PathResolver.getChildren() queries with BOTH sourceId AND verbType:
  getRelations({ from: dirId, type: VerbType.Contains })

This combination wasn't optimized, so it fell through to the
getVerbsWithPagination() path, which MemoryStorage doesn't implement,
causing it to return empty results.

Fix: Added optimization for sourceId + verbType combination
- Uses O(1) graph index lookup for sourceId
- Filters results by verbType in O(n)
- Enables VFS readdir() to work correctly

This was the real bug preventing Workshop team from seeing their
567 markdown files in vfs.readdir('/').

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/storage/baseStorage.ts

@@ -631,6 +631,46 @@ export abstract class BaseStorage extends BaseStorageAdapter {
 
     // Optimize for common filter cases to avoid loading all verbs
     if (options?.filter) {
+      // CRITICAL VFS FIX: If filtering by sourceId + verbType (most common VFS pattern!)
+      // This is the query PathResolver.getChildren() uses: getRelations({ from: dirId, type: VerbType.Contains })
+      if (
+        options.filter.sourceId &&
+        options.filter.verbType &&
+        !options.filter.targetId &&
+        !options.filter.service &&
+        !options.filter.metadata
+      ) {
+        const sourceId = Array.isArray(options.filter.sourceId)
+          ? options.filter.sourceId[0]
+          : options.filter.sourceId
+
+        const verbType = Array.isArray(options.filter.verbType)
+          ? options.filter.verbType[0]
+          : options.filter.verbType
+
+        // Get verbs by source, then filter by type (O(1) graph lookup + O(n) type filter)
+        const verbsBySource = await this.getVerbsBySource_internal(sourceId)
+        const filteredVerbs = verbsBySource.filter(v => v.verb === verbType)
+
+        // Apply pagination
+        const paginatedVerbs = filteredVerbs.slice(offset, offset + limit)
+        const hasMore = offset + limit < filteredVerbs.length
+
+        // Set next cursor if there are more items
+        let nextCursor: string | undefined = undefined
+        if (hasMore && paginatedVerbs.length > 0) {
+          const lastItem = paginatedVerbs[paginatedVerbs.length - 1]
+          nextCursor = lastItem.id
+        }
+
+        return {
+          items: paginatedVerbs,
+          totalCount: filteredVerbs.length,
+          hasMore,
+          nextCursor
+        }
+      }
+
       // If filtering by sourceId only, use the optimized method
       if (
         options.filter.sourceId &&