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/comprehensive/brainy-v3-complete.test.ts

@@ -605,7 +605,7 @@ describe('Brainy v3.0 Complete Test Suite', () => {
         await brain.add({ data: 'Test', type: NounType.Document })
         await brain.find({ query: 'Test' })
         
-        const stats = await brain.getStatistics()
+        const stats = brain.getStats()
         
         expect(stats).toBeDefined()
         expect(stats.totalNouns).toBeGreaterThanOrEqual(1)
@@ -888,7 +888,7 @@ describe('Brainy v3.0 Complete Test Suite', () => {
     })
     
     it('should provide accurate statistics', async () => {
-      const stats = await brain.getStatistics()
+      const stats = brain.getStats()
       
       expect(stats).toBeDefined()
       expect(stats.totalNouns).toBeGreaterThanOrEqual(5)