feat(audit): P88 PDF-Export via WeasyPrint

GET /api/compliance/agent/snapshots/{id}/pdf liefert application/pdf
mit dem vollen Audit-Mail-Inhalt im A4-Print-Layout (Header mit
Site/Timestamp/Snapshot-ID, Seitenzahlen unten rechts).

check_replay.py liefert jetzt zusaetzlich 'full_html' (nicht nur
500-char-preview), damit der PDF-Renderer das komplette HTML hat.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend-compliance/compliance/api/agent_compliance_check_routes.py

@@ -207,6 +207,28 @@ async def get_snapshot(snapshot_id: str):
         db.close()
 
 
+@router.get("/snapshots/{snapshot_id}/pdf")
+async def export_snapshot_pdf(snapshot_id: str):
+    """P88 — PDF-Export der Audit-Mail. Liefert application/pdf."""
+    from fastapi import HTTPException
+    from fastapi.responses import Response
+    from database import SessionLocal
+    from compliance.services.mail_pdf_export import render_snapshot_as_pdf
+    db = SessionLocal()
+    try:
+        pdf = render_snapshot_as_pdf(db, snapshot_id)
+    finally:
+        db.close()
+    if not pdf:
+        raise HTTPException(404, f"Snapshot {snapshot_id} nicht gefunden "
+                                  "oder PDF-Render fehlgeschlagen.")
+    fname = f"breakpilot-audit-{snapshot_id[:8]}.pdf"
+    return Response(
+        content=pdf, media_type="application/pdf",
+        headers={"Content-Disposition": f'attachment; filename="{fname}"'},
+    )
+
+
 @router.post("/snapshots/{snapshot_id}/replay")
 async def replay_snapshot(
     snapshot_id: str,