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>

scripts/install-pi.sh

@@ -46,7 +46,7 @@ User=$USER_NAME
 PAMName=login
 TTYPath=/dev/tty1
 ExecStartPre=/bin/sh -c 'until curl -sf http://localhost:8080/ >/dev/null; do sleep 1; done'
-ExecStart=/usr/bin/cage -- $DIR/scripts/kiosk.sh
+ExecStart=/usr/bin/cage -- /bin/bash $DIR/scripts/kiosk.sh
 Restart=always
 
 [Install]