Added bulk selection and update functionality for customer hourly rates:
Frontend (customers.html):
- Added checkbox column with select-all functionality
- Created bulk price update modal with customer list
- Implemented JavaScript for selection state management
- Shows selected count in UI badge
- Supports indeterminate state for partial selection
Backend (router.py):
- New POST /api/v1/timetracking/customers/bulk-update-rate endpoint
- Accepts {customer_ids: List[int], hourly_rate: float}
- Updates multiple customers in single SQL query
- Creates audit log entries for each updated customer
- Returns updated count
Use case: Select multiple customers and update hourly rate simultaneously
