- Add current_holdings parameter to generate_playbook() and _build_prompt()
- Inject '## Current Holdings' section into Gemini prompt with qty, entry
price, unrealized PnL%, and holding days for each held position
- Instruct AI to generate SELL/HOLD scenarios for held stocks even if not
in scanner candidates list
- Allow held stock codes in _parse_response() valid_codes set so AI-
generated SELL scenarios for holdings pass validation
- Add 6 tests covering prompt inclusion, omission, and response parsing
Closes#170
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>