Add TypeORM entity and DTOs for Projects timesheets feature:
- TimesheetEntity with all fields matching DDL schema
- Extended DTOs for bulk operations (submit, approve, reject)
- Summary types for reporting (by project, user, task)
- Updated module exports to include new files
Complements existing timesheets.service.ts implementation.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
