0.10.4 — spec-rejection + metric-overflow hardening (result_hash unchanged)

Robustness release — result_hash UNCHANGED, ENGINE_VERSION stays 0.9.0 (every hash byte-identical for valid specs; the new paths only affect inputs that previously raised).

• Malformed conditions return a clean blocked verdict instead of raising (#49): empty all_of, unknown/typo operator keys (gt vs gte), bare feature nodes, empty {} when-nodes, malformed feature_equal — previously an uncaught ValueError (HTTP 500 via the prod shim), now E_EVIDENCE_SPEC_INVALID.
• Metric overflow hardening (#49): a denormal entry_price (e.g. 1e-203) drove returns to ~1e+200 → OverflowError. PM / standard (Sharpe/Sortino) / PSR / permutation now degrade the affected field to null instead of raising.

Packaged via #50.