Prevents players who are already claimed in another team's pending
transaction (frozen=false, cancelled=false) from being added to a new
transaction for the same week.
Changes:
- Add is_player_in_pending_transaction() to TransactionService
- Make TransactionBuilder.add_move() async with validation
- Add check_pending_transactions flag (default True for /dropadd)
- Skip validation for /ilmove and trades (check_pending_transactions=False)
- Add tests/conftest.py for proper test isolation
- Add 4 new tests for pending transaction validation
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
