feat: remove legacy ImportManager, standardize getStats() API

- Removed ImportManager class and exports (use brain.import() instead)
- Fixed all documentation: getStatistics() → getStats()
- Updated 41 files across codebase for consistency
- Removed ImportManager section from API docs
- Added v3.30.0 migration guide to CHANGELOG

Co-Authored-By: Claude <noreply@anthropic.com>

tests/benchmarks/quick-verify.js

@@ -51,7 +51,7 @@ async function quickVerify() {
   console.log(`✅ Added verb: ${verbId}`)
   
   // Test 5: Get statistics
-  const stats = await brain.getStatistics()
+  const stats = brain.getStats()
   console.log(`✅ Stats: ${stats.totalNouns} nouns, ${stats.totalVerbs} verbs`)
   
   // Verify real implementations