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>

examples/tests/test-production-ready.js

@@ -176,7 +176,7 @@ async function testProductionFunctionality() {
     console.log('\n8️⃣ Testing statistics and monitoring...')
     try {
       const stats = await withTimeout(
-        brain.getStatistics(),
+        Promise.resolve(brain.getStats()),
         'Statistics retrieval',
         5000
       )