feat(corroboration): wire approval gate + backfill driver + rebuild tool (X11 Phase 2)

- db: approve_halacha_by_corroboration (pending_review→approved only),
  demote_halacha_overruled (approved→pending_review only), list_corroboration_grouped,
  precedents_with_halachot_and_incoming_citations
- corroboration: reconcile_approvals (INV-COR2/COR4/COR5), build_all backfill;
  build_for_precedent now returns approved/demoted counts
- mcp: corroboration_rebuild write tool (single precedent or full-corpus backfill)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

mcp-server/src/legal_mcp/server.py

@@ -934,6 +934,17 @@ async def halacha_corroboration(halacha_id: str) -> dict:
     return {"halacha_id": halacha_id, "summary": agg, "citations": links}
 
 
+@mcp.tool()
+async def corroboration_rebuild(case_law_id: str = "") -> dict:
+    """בנה/רענן את ה-corroboration ויישם אישור-אוטומטי. ריק = כל הקורפוס (backfill);
+    מזהה-תקדים = תקדים בודד. כותב halacha_citation_corroboration ומעדכן review_status
+    (corroborated→approved, overruled→pending_review). X11 Phase 2."""
+    from legal_mcp.services import corroboration as cor
+    if case_law_id.strip():
+        return await cor.build_for_precedent(case_law_id.strip())
+    return await cor.build_all()
+
+
 def main():
     mcp.run(transport="stdio")