feat(t3_code): add T3 Code AppImage launcher and desktop entry

users/richie/home/gui/t3_code/launch.sh

@@ -0,0 +1,25 @@
+# Launch the newest T3 Code AppImage in the app image directory.
+#
+# The nightly builds carry the version in the file name, so the file to run is
+# resolved at launch time rather than baked into the desktop entry.
+# No shebang: this is wrapped by writeShellApplication, which supplies one.
+
+dir="${T3_CODE_DIR:-$HOME/app_images}"
+
+shopt -s nullglob
+images=("$dir"/T3-Code-*.AppImage)
+
+if [ "${#images[@]}" -eq 0 ]; then
+  msg="No T3 Code AppImage found in $dir"
+  echo "$msg" >&2
+  # launched from KDE there is no terminal to read, so say it on screen too
+  kdialog --error "$msg" || true
+  exit 1
+fi
+
+img="$(printf '%s\n' "${images[@]}" | sort -V | tail -n1)"
+[ -x "$img" ] || chmod +x "$img"
+
+# --no-sandbox matches the AppImage's own desktop entry; binfmt hands the
+# AppImage off to appimage-run.
+exec "$img" --no-sandbox "$@"