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-no-search.js

@@ -50,7 +50,7 @@ async function testNoSearch() {
     console.log(`✅ Found ${verbs.length} verb(s) from TypeScript`)
 
     console.log('\n6. Checking statistics...')
-    const stats = await brain.getStatistics()
+    const stats = brain.getStats()
     console.log(`✅ Stats: ${stats.nounCount} nouns, ${stats.verbCount} verbs`)
 
     console.log('\n7. Memory check...')