fix: move Chromium download to Docker build phase

- Download Chromium from Google snapshots during Docker build (network works there)
- Chroot hook now only verifies and installs runtime dependencies
- Remove generated files from repo (OVMF_VARS.fd, qemu.pid, screenshots)
- Update isotest scripts to use .nogit/ directory structure
- Chromium kiosk verified working with Sway compositor

isotest/stop.sh

@@ -1,16 +1,20 @@
 #!/bin/bash
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+PROJECT_ROOT="$SCRIPT_DIR/.."
+VM_DIR="$PROJECT_ROOT/.nogit/vm"
+PID_FILE="$VM_DIR/qemu.pid"
 
-if [ -f "$SCRIPT_DIR/qemu.pid" ]; then
-    PID=$(cat "$SCRIPT_DIR/qemu.pid")
+if [ -f "$PID_FILE" ]; then
+    PID=$(cat "$PID_FILE")
     if kill -0 "$PID" 2>/dev/null; then
         echo "Stopping QEMU (PID: $PID)..."
         kill "$PID"
         sleep 1
     fi
-    rm -f "$SCRIPT_DIR/qemu.pid"
-    rm -f "$SCRIPT_DIR/qemu-monitor.sock"
+    rm -f "$PID_FILE"
+    rm -f "$VM_DIR/qemu-monitor.sock"
+    rm -f "$VM_DIR/serial.sock"
     echo "QEMU stopped"
 else
     echo "QEMU not running (no PID file)"