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/storage/cow/CommitLog.ts

@@ -43,7 +43,7 @@ export interface CommitLogStats {
 /**
  * CommitLog: Efficient commit history traversal and querying
  *
- * Pure v5.0.0 implementation - modern, clean, fast
+ * Pure implementation - modern, clean, fast
  */
 export class CommitLog {
   private blobStorage: BlobStorage