feat: Cookie Banner Check as standalone tab in Compliance Agent

New "Banner-Check" tab with:
- URL input → Playwright 3-phase test (before/reject/accept)
- Shield icon + provider detection
- Progress bar with pass/fail percentage
- 3-phase summary (cookies + scripts per phase)
- Violations (red) and passes (green) in structured list

Backend: new POST /api/compliance/agent/banner-check endpoint
that proxies to consent-tester:8094/scan.

Next step: Upgrade banner checks to L1/L2 format with expert
hints (same quality as document checks).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-compliance/compliance/api/agent_doc_check_routes.py

@@ -92,6 +92,26 @@ class DocCheckStatusResponse(BaseModel):
     error: str = ""
 
 
+class BannerCheckRequest(BaseModel):
+    url: str
+
+
+@router.post("/banner-check")
+async def run_banner_check(req: BannerCheckRequest):
+    """Run cookie banner compliance check via consent-tester."""
+    try:
+        async with httpx.AsyncClient(timeout=120.0) as client:
+            resp = await client.post(
+                f"{CONSENT_TESTER_URL}/scan",
+                json={"url": req.url, "timeout_per_phase": 10},
+            )
+            if resp.status_code == 200:
+                return resp.json()
+            return {"error": f"Consent-Tester: HTTP {resp.status_code}"}
+    except Exception as e:
+        return {"error": str(e)[:200]}
+
+
 @router.post("/doc-check")
 async def start_doc_check(req: DocCheckRequest):
     """Start async multi-URL document check."""