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.

docs/guides/import-flow.md

@@ -39,7 +39,7 @@ Each phase adds intelligence and structure to your raw data, transforming it int
 
 ---
 
-## 🌊 Always-On Streaming Architecture (v4.2.0+)
+## 🌊 Always-On Streaming Architecture
 
 All imports use streaming with **progressive flush intervals**:
 
@@ -1062,7 +1062,7 @@ if (!fromEntity || !toEntity) {
 }
 ```
 
-#### 5.3b: Check for Duplicates (v3.43.2 Critical Fix)
+#### 5.3b: Check for Duplicates (Critical Fix)
 
 **The Bug**: Without duplicate checking, re-importing would create:
 ```