fix(kasm): replace removed apt-key, fix kasm_release URL, drop missing thumbnails

The kasm release build (run 25485774052) failed at the very first
'apt-key add -' invocation because apt-key was removed from the new
Ubuntu 26.04 (resolute) base image. Two further upstream changes were
also broken:

- The Docker GPG key is now imported via gpg --dearmor into
  /usr/share/keyrings and referenced through 'signed-by=' in the
  docker.list source, matching the modern keyring pattern.
- The kasm_release tarball is no longer published as a GitHub release
  asset on kasmtech/kasm-install-wizard; switch to the official
  https://kasm-static-content.s3.amazonaws.com/kasm_release_<ver>.tar.gz
  URL used by upstream installer / linuxserver.
- Drop the docker-image-preload step (kasm-ci.s3 images-combined
  tarball no longer exists for current versions and is fetched at
  runtime by Kasm itself), and remove the obsolete www/img/thumbnails
  copy + yq tweak (the thumbnails directory no longer exists in the
  kasm_release tarball).

Co-authored-by: Crow-Control <7613738+Crow-Control@users.noreply.github.com>

Author: actions-user

apps/kasm/Dockerfile

@@ -16,8 +16,9 @@ ENV NVIDIA_DRIVER_CAPABILITIES="compute,graphics,video,utility"
 # Container setup
 RUN \
   echo "**** install packages ****" && \
-  curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add - && \
-  echo "deb [arch=$TARGETARCH] https://download.docker.com/linux/ubuntu noble stable" > \
+  install -d -m 0755 /usr/share/keyrings && \
+  curl -fsSL https://download.docker.com/linux/ubuntu/gpg | gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg && \
+  echo "deb [arch=$TARGETARCH signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu noble stable" > \
     /etc/apt/sources.list.d/docker.list && \
   curl -fsSL https://nvidia.github.io/libnvidia-container/gpgkey | gpg --dearmor -o /usr/share/keyrings/nvidia-container-toolkit-keyring.gpg \
     && curl -s -L https://nvidia.github.io/libnvidia-container/stable/deb/nvidia-container-toolkit.list | \
@@ -72,29 +73,17 @@ RUN \
   echo "**** add installer ****" && \
   curl -o \
     /tmp/kasm.tar.gz -L \
-    "https://github.com/kasmtech/kasm-install-wizard/releases/download/${VERSION}/kasm_release.tar.gz" && \
+    "https://kasm-static-content.s3.amazonaws.com/kasm_release_${VERSION}.tar.gz" && \
   tar xf \
     /tmp/kasm.tar.gz -C \
     / && \
   ALVERSION=$(cat /kasm_release/conf/database/seed_data/default_properties.yaml |awk '/alembic_version/ {print $2}') && \
-  curl -o \
-    /tmp/images.tar.gz -L \
-    "https://kasm-ci.s3.amazonaws.com/${VERSION}-images-combined.tar.gz" && \
-  tar xf \
-    /tmp/images.tar.gz -C \
-    / && \
   sed -i \
     '/alembic_version/s/.*/alembic_version: '${ALVERSION}'/' \
     /kasm_release/conf/database/seed_data/default_images_a* && \
   sed -i 's/-N -e -H/-N -B -e -H/g' /kasm_release/upgrade.sh && \
   echo "exit 0" > /kasm_release/install_dependencies.sh && \
-  /kasm_release/bin/utils/yq_$(uname -m) -i \
-    '.services.proxy.volumes += "/kasm_release/www/img/thumbnails:/srv/www/img/thumbnails"' \
-    /kasm_release/docker/docker-compose-all.yaml && \
   echo "**** copy assets ****" && \
-  cp \
-    /kasm_release/www/img/thumbnails/*.png /kasm_release/www/img/thumbnails/*.svg \
-    /wizard/public/img/thumbnails/ && \
   cp \
     /kasm_release/conf/database/seed_data/default_images_a* \
     /wizard/ && \