fix(types): resolve TypeScript unused variable errors

Fix all TS6133 errors (unused variables) across service layer:

- Remove unused imports (path, ExtractionProgress type)
- Prefix unused parameters with underscore (_session, _totalBatches, etc.)
- Remove unused _verbose field and constructor from ExcelParser
- Remove unused _importToDatabase method from ExtractorService
- Remove unused _importProgress variable

This ensures clean type checking and eliminates dead code.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/main/services/database/data-importer.ts

@@ -9,7 +9,6 @@
  * 4. Batch insert new records
  */
 
-import path from 'path'
 import { createLogger } from '../logger'
 import { DiscreteMaterialPlanDAO, type MaterialPlanRecord } from './discrete-material-plan-dao'