fix: resolve 10 test failures across clustering, metadata, and deletion

Fixed critical bugs affecting test suite:

**Clustering (2 tests fixed)**
- Fixed entity.type field reference bug in _getItemsByField()
- Changed entity.noun to entity.type (correct Entity interface field)
- Now includes ALL entities in domain clustering with 'unknown' fallback

**Relationship Metadata (5 tests fixed)**
- Fixed metadata retrieval in memoryStorage.ts getVerbs()
- Changed metadata.data to metadata.metadata for user's custom metadata
- User metadata now correctly returned in GraphVerb.metadata field

**Delete Relationship Cleanup (2 tests fixed)**
- Added deleteVerbMetadata() method to BaseStorage
- Fixed deleteVerb_internal() in memoryStorage to delete verb metadata
- Relationships now properly cleaned up when entities are deleted

**Validation (1 test fixed)**
- Removed overly restrictive self-referential relationship check
- Self-relationships now allowed (valid in graph systems)

Test results: 27 failures → 17 failures (37% improvement)
All 467 tests now enabled (0 skipped)

src/storage/baseStorage.ts

@@ -920,6 +920,16 @@ export abstract class BaseStorage extends BaseStorageAdapter {
     return this.readObjectFromPath(keyInfo.fullPath)
   }
 
+  /**
+   * Delete verb metadata from storage
+   * Uses routing logic to handle both UUIDs (sharded) and system keys (unsharded)
+   */
+  public async deleteVerbMetadata(id: string): Promise<void> {
+    await this.ensureInitialized()
+    const keyInfo = this.analyzeKey(id, 'verb-metadata')
+    return this.deleteObjectFromPath(keyInfo.fullPath)
+  }
+
   /**
    * Save a noun to storage
    * This method should be implemented by each specific adapter