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/focused-validation.js

@@ -57,7 +57,7 @@ try {
   const searchResults = await brain.search('test', { limit: 1 })
   console.log(`✅ [${timeElapsed()}s] Search returned ${searchResults.length} results`)
   
-  const stats = await brain.getStatistics()
+  const stats = brain.getStats()
   console.log(`✅ [${timeElapsed()}s] Statistics: ${stats.nounCount} nouns`)
   
   console.log(`\n🎉 COMPLETE SUCCESS in ${timeElapsed()}s!`)