feat: make local-search arms optimize on a COP (SA annealing, objective-bound ratchet)

[rasros]

Derived from #928, which framed this as an explicit feasibility-finder vs optimizer role split. This takes the opposite approach: every local-search arm optimizes on a COP, so there is no finder role to make explicit.

What changed

• SA arms drive objective descent past feasibility. A new SourceDrivenStrategy.ownsFeasibleDescent seam lets Metropolis own the feasible-phase walk instead of the engine's greedy strict-improvement gate reverting its exploratory moves.
• Violation-native arms (probSAT, WalkSAT, feasibility-jump) optimize a COP by repairing an objective ≤ incumbent constraint (ObjectiveBoundFactor) overlaid on the arm's problem and tightened at each incumbent, turning objective descent back into violation repair.
• The portfolio applies this automatically in materialize: on a COP a descent-driving recipe is left as-is and every other arm gets the ratchet, so no arm bails at feasibility. A CSP leaves every arm a pure feasibility finder. No per-arm flag, no duplicate arms.

Why

On a COP the SAT-style feasibility arms discarded their accumulated landscape state at cost == 0 and handed the objective to a generic greedy tail. Each arm now optimizes with its own machinery, so the feasibility fight's information carries into the optimize phase.

Testing

• SA anneals a small COP to its optimum; probSAT ratchets a COP to its optimum by repairing the bound factor.
• Smoke A/B on the curated mzn-bench COP set: the arms reach feasibility and optimize (e.g. the ratchet reaches 194018 on evilshop vs plain probSAT's 237571).