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)

tests/integration/brainy-complete.integration.test.ts

@@ -148,12 +148,7 @@ describe('Brainy 2.0 Complete Feature Test (Real AI)', () => {
     })
   })
 
-// TODO: Implement NLP features for find() method
-// - Natural language query processing
-// - Pattern library integration
-// Expected completion: 3-4 weeks
-
-  describe.skip('2. find() with NLP and Pattern Library - SKIPPED: NLP features not yet implemented', () => {
+  describe('2. find() with NLP and Pattern Library', () => {
     it('should handle natural language queries with find()', async () => {
       console.log('🗣️ Testing find() with natural language queries...')