feat: gate author work on early duplicate-work detection (Closes #400)

Add author_duplicate_work_gate and enforce it at claim, lock, and PR
creation. Expose gitea_assess_author_duplicate_work for pre-commit/push
checks and extend work-issue final-report verification.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

review_proofs.py

@@ -3612,18 +3612,33 @@ def assess_work_issue_mode_isolation(report_text: str) -> dict:
     }
 
 
+def assess_work_issue_duplicate_prevention_report(report_text, **kwargs):
+    """#400: work-issue reports must classify duplicate-work prevention."""
+    from author_duplicate_work_gate import (
+        assess_work_issue_duplicate_prevention_report as _assess,
+    )
+
+    return _assess(report_text, **kwargs)
+
+
 def assess_work_issue_final_report(report_text: str) -> dict:
     """#139: composite verifier for work-issue final reports."""
     checks = {
         "workflow_source": assess_work_issue_workflow_source(report_text),
         "mode_isolation": assess_work_issue_mode_isolation(report_text),
+        "duplicate_prevention": assess_work_issue_duplicate_prevention_report(
+            report_text
+        ),
     }
 
     reasons = []
     downgraded = False
     for name, result in checks.items():
         verdict = result.get("verdict")
-        if verdict in ("missing", "incomplete"):
+        if result.get("block"):
+            downgraded = True
+            reasons.extend(result.get("reasons") or [])
+        elif verdict in ("missing", "incomplete"):
             downgraded = True
             reasons.extend(result.get("reasons") or [])
         elif result.get("downgraded") or not result.get("complete", True):
@@ -3631,6 +3646,9 @@ def assess_work_issue_final_report(report_text: str) -> dict:
             reasons.extend(
                 f"{name}: {r}" for r in (result.get("reasons") or [])
             )
+        elif result.get("proven") is False:
+            downgraded = True
+            reasons.extend(result.get("reasons") or [])
 
     grade = "A" if not downgraded else "downgraded"
     return {