feat: refocus on drawings — code/ADA gated off, drawing-integrity wave, Brain-directed clarification

- ENABLE_CODE_REVIEW flag (default off): skips code/ADA/jurisdiction review
  path in both pipelines; nothing deleted, one env flag to restore.
- Per-sheet Drawing Integrity QA wave (agent + classic, default on):
  dangling refs, on-sheet contradictions, dimension sanity, missing sheet
  essentials, tag hygiene. New DrawingIntegrityAgent + classic stage.
- Broadened conflict critic: intra-sheet + same-discipline contradictions,
  not just cross-discipline.
- Wave 6.5 Brain-directed clarification (bounded hub-and-spoke): Brain names
  uncertain findings, verify_evidence requests route through the wave-5b
  verifier; refuted findings suppressed. One planning call + capped verifies,
  single iteration. Shared _build_verify_scopes across 5b and 6.5.
- Config knobs, .env.example, frontend copy, tests (182 passing).

tests/agents/test_runner_review_gate.py

@@ -4,7 +4,7 @@ from backend.agents.runner import run_agent_pipeline
 
 def _patch_brain(monkeypatch):
     monkeypatch.setattr("backend.agents.runner.convert_pdf_to_images", lambda path: [{"page_number": 1, "base64": "x"}])
-    monkeypatch.setattr("backend.agents.runner.BrainAgent", lambda usage: type("B", (), {"run": lambda self, findings, sheet_index, jurisdiction: ([{"issue_id": "AGENT-0001", "severity": "high", "confidence": "high", "category": "note_or_spec_contradiction", "source_stage": "conflict"}], [])})())
+    monkeypatch.setattr("backend.agents.runner.BrainAgent", lambda usage: type("B", (), {"run": lambda self, findings, sheet_index, jurisdiction: ([{"issue_id": "AGENT-0001", "severity": "high", "confidence": "high", "category": "note_or_spec_contradiction", "source_stage": "conflict"}], []), "plan_clarifications": lambda self, prioritized: []})())
 
 
 def test_agent_runner_can_enter_review_mode(monkeypatch, tmp_path):