Update test fixtures to current runtime contracts (#14259)

Recent runtime changes left the aggregate suite expecting a VS Code symlink and fixed extension version, pacman arguments without the end-of-options marker, a one-argument QML text signal, and background functions without preparation state. Align these fixtures with the current interfaces while retaining palette equality, package retry, keyboard action, and missing-background recovery assertions.

Co-authored-by: Omarchybot <317366263+omarchybot@users.noreply.github.com>

test/shell.d/video-background-test.sh

@@ -331,6 +331,8 @@ video_snapshot=$(snapshot_background_path "$CURRENT_THEME_PATH/backgrounds/old.m
 CHOSEN_THEME_BACKGROUND="$transition_home/disappeared.mp4"
 BACKGROUND_TRANSITION_SNAPSHOTS=false
 OLD_BACKGROUND_SNAPSHOT=""
+PREPARED_BACKGROUND=""
+PREPARED_BACKGROUND_SNAPSHOT=""
 colors_payload=""
 shell_payload=""
 shell_ipc() { :; }