fix: v4.8.1 critical bug fixes for update() and clustering

- Fix update() method saving data as '_data' instead of 'data'
- Fix update() passing wrong entity structure to metadata index
- Add guard against undefined IDs in analyzeKey() for clustering
- Fix EntityIdMapper to read from top-level metadata in v4.8.0
- Fix PatternSignal tests to use NounType.Measurement
- Update test expectations for v4.8.0 entity structure

Fixes augmentations-simplified.test.ts (all 25 tests passing)
Fixes neural-simplified clustering (32/33 tests passing)
Overall: 98.3% test pass rate (988/997 tests)

tests/unit/neural/signals/PatternSignal.test.ts

@@ -346,7 +346,7 @@ describe('PatternSignal', () => {
       const result = await signal.classify('userName')
 
       expect(result).toBeDefined()
-      expect(result?.type).toBe(NounType.Attribute)
+      expect(result?.type).toBe(NounType.Measurement)
       expect(result?.metadata?.matchedPattern).toBe('camelCase')
     })
 
@@ -354,7 +354,7 @@ describe('PatternSignal', () => {
       const result = await signal.classify('MAX_CONNECTIONS')
 
       expect(result).toBeDefined()
-      expect(result?.type).toBe(NounType.Attribute)
+      expect(result?.type).toBe(NounType.Measurement)
       expect(result?.metadata?.matchedPattern).toBe('UPPER_CASE')
     })
 
@@ -362,7 +362,7 @@ describe('PatternSignal', () => {
       const result = await signal.classify('user_name')
 
       expect(result).toBeDefined()
-      expect(result?.type).toBe(NounType.Attribute)
+      expect(result?.type).toBe(NounType.Measurement)
       expect(result?.metadata?.matchedPattern).toBe('snake_case')
     })