Pi: fix kiosk WebGL2 (hardware V3D via ANGLE) + robust kiosk launch

- Drop --use-gl=egl (disabled the GPU on Chromium 149) and let Chromium pick the
  default ANGLE/GLES backend with --ignore-gpu-blocklist -> hardware WebGL2.
- Launch kiosk via 'cage -- bash kiosk.sh' so a non-executable bit after rsync
  no longer breaks startup.
- output.js reports gpuInfo (webgl2 + renderer) on load for remote diagnostics.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/js/output.js

@@ -8,7 +8,13 @@ const canvas = $('#gl');
 let viz;
 try {
   viz = new Visualizer(canvas);
+  try {
+    const gl = canvas.getContext('webgl2');
+    const d = gl && gl.getExtension('WEBGL_debug_renderer_info');
+    djv.report({ type: 'gpuInfo', webgl2: !!gl, renderer: d ? gl.getParameter(d.UNMASKED_RENDERER_WEBGL) : (gl && gl.getParameter(gl.RENDERER)) });
+  } catch (e2) {}
 } catch (e) {
+  djv.report({ type: 'gpuInfo', webgl2: false, message: e.message });
   document.body.innerHTML = '<div style="color:#fff;padding:40px;font-family:sans-serif">' +
     'Errore grafica:<br><pre>' + e.message + '</pre></div>';
   throw e;