- Apply _PRICE_EXCHANGE_MAP in get_overseas_price() to send short codes
(NASD→NAS, NYSE→NYS, AMEX→AMS) required by HHDFS00000300 price API
- Add PAPER_OVERSEAS_CASH config setting (default $50,000) for simulated
USD balance when VTS overseas balance API returns 0 in paper mode
- Fall back to scan candidate price when live price API returns 0
- Both fixes together resolve "no affordable quantity (cash=0, price=0)"
which was preventing all overseas trade execution
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>