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/unit/neural/neural-simplified.test.ts

@@ -96,7 +96,7 @@ describe('Neural API - Production Testing', () => {
     })
   })
 
-  describe.skip('3. Basic Clustering', () => {
+  describe('3. Basic Clustering', () => {
     it('should perform basic clustering with no items', async () => {
       const clusters = await brain.neural().clusters()
       expect(Array.isArray(clusters)).toBe(true)
@@ -148,7 +148,7 @@ describe('Neural API - Production Testing', () => {
     })
   })
 
-  describe.skip('4. Domain-Aware Clustering', () => {
+  describe('4. Domain-Aware Clustering', () => {
     it('should cluster by metadata domain', async () => {
       // Add entities with different categories
       await brain.add(createAddParams({
@@ -214,7 +214,7 @@ describe('Neural API - Production Testing', () => {
     })
   })
 
-  describe.skip('6. Semantic Hierarchy', () => {
+  describe('6. Semantic Hierarchy', () => {
     it('should build hierarchy for entity', async () => {
       const id = await brain.add(createAddParams({
         data: 'Root concept for hierarchy'
@@ -242,7 +242,7 @@ describe('Neural API - Production Testing', () => {
     })
   })
 
-  describe.skip('7. Outlier Detection', () => {
+  describe('7. Outlier Detection', () => {
     it('should detect outliers in dataset', async () => {
       // Add some normal documents
       await brain.add(createAddParams({ data: 'Normal document about AI' }))
@@ -305,7 +305,7 @@ describe('Neural API - Production Testing', () => {
     })
   })
 
-  describe.skip('9. Incremental Clustering', () => {
+  describe('9. Incremental Clustering', () => {
     it('should update clusters with new items', async () => {
       // Create initial entities
       const id1 = await brain.add(createAddParams({ data: 'Initial cluster item 1' }))
@@ -329,7 +329,7 @@ describe('Neural API - Production Testing', () => {
     })
   })
 
-  describe.skip('10. Advanced Clustering Features', () => {
+  describe('10. Advanced Clustering Features', () => {
     it('should perform clustering with relationships', async () => {
       // Add entities with potential relationships
       const id1 = await brain.add(createAddParams({ data: 'Entity with relationships 1' }))
@@ -361,7 +361,7 @@ describe('Neural API - Production Testing', () => {
     })
   })
 
-  describe.skip('11. Streaming Clustering', () => {
+  describe('11. Streaming Clustering', () => {
     it('should handle streaming clustering', async () => {
       // Add test data
       const promises = Array.from({ length: 10 }, (_, i) =>
@@ -393,7 +393,7 @@ describe('Neural API - Production Testing', () => {
         .rejects.toThrow()
     })
 
-    it.skip('should handle invalid clustering options', async () => {
+    it('should handle invalid clustering options', async () => {
       const clusters = await brain.neural().clusters({
         minClusterSize: -1, // Invalid
         maxClusters: 0 // Invalid
@@ -409,7 +409,7 @@ describe('Neural API - Production Testing', () => {
     })
   })
 
-  describe.skip('13. Performance and Scalability', () => {
+  describe('13. Performance and Scalability', () => {
     it('should handle moderate dataset sizes efficiently', async () => {
       // Create 50 entities
       const promises = Array.from({ length: 50 }, (_, i) =>