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-core-direct.js

@@ -90,7 +90,7 @@ async function testBrainyCore() {
     
     // Test 9: Statistics
     console.log('\n📊 Testing Statistics')
-    const stats = await brain.getStatistics()
+    const stats = brain.getStats()
     assert(typeof stats.totalItems === 'number', 'Should provide total items count')
     assert(stats.totalItems >= 3, 'Should count added items')
     console.log(`   Total items: ${stats.totalItems}`)