fix: do not infer missing crypto weekends from intraday row counts #105

Reproduction

On main c7b9dfa, obtain continuous SyntheticProvider minute OHLCV for BTCUSD on 2025-07-07 and pass its first seven consecutive rows to CryptoSessionValidator().validate_continuity(frame, "minute"). The result is ["Missing weekend data (crypto trades 24/7)"] despite a complete seven-minute Monday interval. AssetValidator's crypto path also consumes this result.

Required correction

Do not infer that an observation window spans a weekend from len(timestamps) >= 7. Retain actual chronological gap detection through the existing CryptoCalendar, including real missing weekend bars, and volume/price validation. This focused false-positive repair does not claim to implement the separate shared calendar-selection migration.

Use actual SyntheticProvider rows, a failing-base/passing-fix regression and complete applicable hosted qualification. No new release or deployment. AI-assisted maintenance under maintainer direction.