feat: phase 1 — data downloader, backtrader runner, SMA strategy

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CLAUDE.md

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+# Chinese Equity Quant Research Framework
+
+## Architecture
+- backtrader is the backtesting engine — never reimplement backtest logic
+- akshare primary data source, baostock secondary fallback
+- Daily frequency only (Phase 1)
+
+## Key Commands
+- `python3 run_example.py` — smoke test
+- `python3 -m pytest tests/ -v` — run tests
+- `pip install -r requirements.txt` — install deps
+
+## Code Standards
+- Type hints on public functions
+- Google-style docstrings
+- 4-space indentation for Python