Remove the HA Dashboard tab and the Qt WebEngine dependency (D40)

DSH-1 ended with a negative result: the Frame's system WebEngine can't be
loaded, and bundling our own failed (no sandbox, ICU resources, Vulkan
abort, empty page). Reverts the tab (60deb43), the container packages
(0676998) and the bundler's WebEngine support (b823ff3, e2cfa8e), and
updates the docs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docker/cross-arm64.Dockerfile

@@ -17,13 +17,4 @@ RUN dpkg --add-architecture arm64 \
         qml6-module-qtquick-layouts:arm64 qml6-module-qtquick-templates:arm64 \
         qml6-module-qtqml-workerscript:arm64 qml6-module-qtquick-window:arm64 \
         qt6-qpa-plugins:arm64 qt6-wayland:arm64 \
-        qt6-webengine-dev:arm64 qml6-module-qtwebengine:arm64 \
  && rm -rf /var/lib/apt/lists/*
-
-# Qt WebEngine's helper process for arm64 (bundled builds): its package is Multi-Arch: foreign
-# and can't be installed next to the amd64 one, so unpack it into its own directory.
-RUN apt-get update \
- && cd /tmp && apt-get download libqt6webenginecore6-bin:arm64 \
- && dpkg-deb -x libqt6webenginecore6-bin_*_arm64.deb /opt/qt6-arm64 \
- && rm -f libqt6webenginecore6-bin_*_arm64.deb && rm -rf /var/lib/apt/lists/* \
- && test -x /opt/qt6-arm64/usr/lib/qt6/libexec/QtWebEngineProcess

docker/native.Dockerfile

@@ -13,5 +13,4 @@ RUN apt-get update \
         qml6-module-qtquick qml6-module-qtquick-controls qml6-module-qtquick-layouts \
         qml6-module-qtquick-templates qml6-module-qtqml-workerscript qml6-module-qtquick-window \
         qml6-module-qttest qt6-qpa-plugins qt6-wayland \
-        qt6-webengine-dev qml6-module-qtwebengine \
  && rm -rf /var/lib/apt/lists/*