#123: harden validation authority matrix foundation

[justsml]

Refs #123

Preserves the blocked v1 manifest and adds a blocked v2 foundation that validates matched quartets independently across models, fixtures, and repeats; separates model refusal/low-quality/budget failures; and reports variance for every deterministic metric, cost, and latency.

Paid execution remains blocked on #100 until strict, auto, self, and yolo have genuinely distinct production behaviors.

[justsml]

Council of Dans review: repair/defer. Highest-priority gate: Remain blocked by a safe #100 authority implementation; repair v1/v2 compatibility and enforce unique complete mode quartets/minimum repeats at the stable public seam. Feature flags are not a substitute for authority, evidence-integrity, or durability fixes; use typed modes only where they provide a real rollout boundary.