fix: extraction, multi-hop traversal, and aggregate result shape (BR-ADV-FEATURES-BUN)

Three advanced-API correctness fixes, all reproducible on Node (not Bun-specific):

- Entity/concept extraction returned []. SmartExtractor combined agreeing signals
  with a weighted sum compared against an absolute 0.60 gate, so a confident
  low-weight signal lost selection to a mediocre high-weight one that then failed
  the gate, dropping the whole result. Select and gate on a normalized weighted
  average instead. The public `confidence` option now controls the threshold (was
  a dead hardcoded 0.60), and the embedding-signal timeout is raised 100ms -> 2000ms
  so the neural signal is not silently dropped on slower runtimes.

- Multi-hop find({ connected }) returned only the 1-hop neighbour. executeGraphSearch
  ignored depth/via; it now delegates to the depth-aware neighbors() BFS.

- find({ aggregate }) hid groupKey/metrics/count under .metadata, so callers
  expecting AggregateResult saw empty rows. Expose those fields at the top level.

Adds real-embedding regression tests in tests/integration/advanced-apis-regression.test.ts.

tests/unit/neural/NaturalLanguageProcessor.test.ts

@@ -118,10 +118,11 @@ describe('NaturalLanguageProcessor', () => {
       expect(extraction).toBeDefined()
       expect(Array.isArray(extraction)).toBe(true)
 
-      // Entity extraction uses neural matching with type embeddings
-      // Extraction quality depends on text context and entity similarity to known types
-      // For simple text without rich context, extraction may return empty array
-      // This is correct behavior - it's better to return nothing than false positives
+      // This unit suite runs with mock (zero-vector) embeddings, so the neural embedding
+      // signal can't fire here — only the array shape is asserted. Real, non-empty extraction
+      // is verified against actual embeddings in
+      // tests/integration/advanced-apis-regression.test.ts (BR-ADV-FEATURES-BUN). An empty
+      // result here reflects the mock embeddings, not expected production behaviour.
     })
     
     it('should extract topics and concepts', async () => {