feat(scoring): act on unmodeled-constant drift (not just report it)

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Found in the 2026-06-17 scoring-sync audit.

Problem

findUnmodeledUpstreamConstants (model.ts:66-74) computes the unmodeled set and pushes a warning, but it's reported-only — exposed on /v1/scoring/model then collapsed to a bare warningCount in audit metadata (routes.ts:935). Nothing alerts or files an issue. The separate ruleset drift system (src/upstream/ruleset.ts) does file GitHub issues but on a different signal.

Deliverable

• Route the model.ts unmodeled-constant set into the Pipeline-B drift surface (or an alert/auto-filed issue, gated by GITTENSORY_AUTO_FILE_DRIFT_ISSUES) so new upstream scoring constants don't silently go unmodeled

Outcome

When upstream adds a scoring constant, we get a tracked signal automatically instead of a buried warning. Milestone M1.