marque-config — layered configuration loading.

Precedence (highest wins): CLI flags → env vars → .marque.local.toml → .marque.toml

Hard-fail validators (T023)

The loader refuses to produce a Config if any of these conditions hold:

• .marque.toml contains a [user] section (FR-010, SC-006) → exit 65
• [capco] version mismatches marque_ism::SCHEMA_VERSION (FR-011) → exit 65
• confidence_threshold outside [0.0, 1.0] → exit 65