fix: exclude __words__ keyword index from corruption detection and getStats()

The __words__ keyword index stores 50-5000 entries per entity (one per
word), which inflated avg entries/entity well above the corruption
threshold of 100. This caused:

1. validateConsistency() to falsely detect corruption on every startup,
   triggering unnecessary clearAllIndexData() + rebuild() cycles
2. getStats() to log false "Metadata index may be corrupted" warnings
   and report inflated totalEntries/totalIds stats

Both methods now skip __words__ when counting, so stats and health
checks reflect metadata fields only (noun, type, createdAt, etc.).
Keyword search is unaffected since the __words__ field index itself
is not modified.

src/index.ts

@@ -70,7 +70,7 @@ export type {
   NeuralImportOptions
 } from './cortex/neuralImport.js'
 
-// Export Neural Entity Extraction (v5.7.6 - Workshop request)
+// Export Neural Entity Extraction
 export { NeuralEntityExtractor } from './neural/entityExtractor.js'
 export { SmartExtractor } from './neural/SmartExtractor.js'
 export { SmartRelationshipExtractor } from './neural/SmartRelationshipExtractor.js'
@@ -220,7 +220,7 @@ export {
 // FileSystemStorage is exported separately to avoid browser build issues
 export { FileSystemStorage } from './storage/adapters/fileSystemStorage.js'
 
-// Export COW (Copy-on-Write) infrastructure for v5.0.0
+// Export COW (Copy-on-Write) infrastructure
 // Enables premium augmentations to implement temporal features
 import { CommitLog } from './storage/cow/CommitLog.js'
 import { CommitObject, CommitBuilder } from './storage/cow/CommitObject.js'
@@ -543,7 +543,7 @@ export type {
   MCPTool
 }
 
-// ============= Integration Hub (v7.4.0) =============
+// ============= Integration Hub =============
 // Connect Brainy to Excel, Power BI, Google Sheets, and more
 // Enable with: new Brainy({ integrations: true })