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)

src/utils/entityIdMapper.ts

@@ -54,8 +54,9 @@ export class EntityIdMapper {
   async init(): Promise<void> {
     try {
       const metadata = await this.storage.getMetadata(this.storageKey)
-      if (metadata && metadata.data) {
-        const data = metadata.data as EntityIdMapperData
+      // v4.8.0: metadata IS the data (no nested 'data' property)
+      if (metadata && (metadata as any).nextId !== undefined) {
+        const data = metadata as any as EntityIdMapperData
         this.nextId = data.nextId
 
         // Rebuild maps from serialized data