feat: enhance crypto DCA strategies with smart sizing, escape, and backtest validation

[Pigbibi]

Summary

Enhances all three crypto strategies with smart features comparable to the IBIT Smart DCA on the US equity side.

Changes

crypto_btc_dca (81→550 lines):

• AHR999 cycle multiplier (bottom 3.0x / accumulation 2.25x / DCA 1.5x / expensive skip)
• Drawdown-based smart sizing (severe 3.0x / deep 2.25x / mild 1.5x)
• Z-score exit (逃顶): MVRV Z-Score → reduce BTC to 50%/25%, park in USDT
• Execution window: monthly day 25 ± 5 days
• Bilingual i18n (Chinese/English)

crypto_trend_rotation:

• Fix empty btc_snapshot bug (was passing {} → rotation never triggered)
• Circuit breaker: suspend trend positions when BTC below SMA200
• Volatility-based position scaling
• i18n signal descriptions

crypto_equity_combo:

• Simplify to pure combinator (~50% code reduction)
• BTC leg now delegates to enhanced smart DCA (was previously bare equity-scaled ratio)

Infrastructure:

• Extract shared utilities to _utils.py (eliminates ~80 lines of duplication)
• Backtest script comparing 5 DCA strategies (2021-2026)
• 35 new unit tests

Backtest Results (2021-2026)

Strategy	Final Value	Calmar
Ordinary DCA	$73,806	6.23
Smart (AHR999)	$154,633	7.88
Smart (Full)	$175,796	6.31

Verification

• 61 unit tests pass
• Backtest validates 2.4x outperformance of smart over ordinary DCA

🤖 Generated with Claude Code