chore: remove dead modules (judge, execution, calibrate, stage_processors, slot_contract)

The reachability-first audit (previous commit) found these five with no
import path from any entry point:

- model/judge.py: replaced by model/pipeline.py, which never imported it.
- model/execution.py: the MGD Req 10 execution seam, never built or called.
- model/calibrate.py: no CLI, no importer; learn/calibrate.py is the live one.
- stage_processors.py + slot_contract.py: kept only so test_gate could pin
  them; the scan runs findings.quick_scan_findings directly.

Their tests go with them, test_gate's zero-dependency list drops the two
entries, the audit lists drop their rows, and the manifest is regenerated:
150 modules, 145 load_bearing, 5 standalone, 0 orphaned.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

tests/test_gate.py

@@ -134,8 +134,6 @@ GOVERNANCE_SCORING_BENCHMARK_PLANES = (
     "openultrasast.ruleset.store",
     "openultrasast.improve",
     "openultrasast.improve.evolve",
-    "openultrasast.slot_contract",
-    "openultrasast.stage_processors",
     "openultrasast.fusion",
     "openultrasast.skills",
     "openultrasast.redaction",