fix(frontend): improve dense QR readability (#6396)

Dense AmneziaWG configs crossed a QR version boundary at the fixed display size, and the generated symbol had no quiet zone. Use low error correction and a four-module margin to reduce module density while keeping the payload unchanged.

frontend/src/pages/inbounds/qr/QrPanel.tsx

@@ -140,6 +140,8 @@ export default function QrPanel({
               className="qr-code"
               value={value}
               size={size}
+              errorLevel="L"
+              marginSize={4}
               type="svg"
               bordered={false}
               color="#000000"