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>

admin-compliance/app/api/sdk/v1/agent/banner-check/route.ts

@@ -0,0 +1,42 @@
+/**
+ * Banner Check API Proxy — calls consent-tester /scan endpoint
+ *
+ * POST /api/sdk/v1/agent/banner-check → runs 3-phase cookie banner test
+ */
+
+import { NextRequest, NextResponse } from 'next/server'
+
+const BACKEND_URL = process.env.BACKEND_API_URL || 'http://backend-compliance:8002'
+
+export async function POST(request: NextRequest) {
+  try {
+    const body = await request.json()
+    const { url } = body
+
+    if (!url) {
+      return NextResponse.json({ error: 'URL erforderlich' }, { status: 400 })
+    }
+
+    // Call backend which proxies to consent-tester
+    const response = await fetch(`${BACKEND_URL}/api/compliance/agent/banner-check`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ url }),
+      signal: AbortSignal.timeout(120000), // 2 min for Playwright
+    })
+
+    if (!response.ok) {
+      const errorText = await response.text()
+      return NextResponse.json(
+        { error: `Backend: ${response.status}`, detail: errorText },
+        { status: response.status },
+      )
+    }
+
+    const data = await response.json()
+    return NextResponse.json(data)
+  } catch (error) {
+    const msg = error instanceof Error ? error.message : 'Unknown error'
+    return NextResponse.json({ error: msg }, { status: 500 })
+  }
+}