Skip shell tests when the compositor can't be reached (#6749)

* Skip shell tests when the compositor can't be reached, not just when WAYLAND_DISPLAY is unset

A set variable only proves the environment was inherited. Sandboxes pass it
through while blocking $XDG_RUNTIME_DIR, so Quickshell cleared the guard and
aborted inside QGuiApplication, leaving two core dumps per launch instead of a
clean skip. Probe the socket and, when there's a signature to ask with,
Hyprland itself. Disable core dumps on the way through for the compositor that
dies mid-run, which no probe can catch.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

* Retry the compositor query before calling it dead

Hyprland can miss a query while it reconfigures outputs, and one miss was enough
to skip a whole file's runtime coverage. Retry the way omarchy-launch-shell
does. Only a leftover socket reaches the query at all, so the ordinary skip
still returns immediately.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

test/shell.d/indicator-contract-test.sh

@@ -18,10 +18,7 @@ cleanup() {
 }
 trap cleanup EXIT
 
-if [[ -z ${WAYLAND_DISPLAY:-} ]]; then
-  pass "no Wayland compositor; skipping QML contract test"
-  exit 0
-fi
+require_compositor "QML contract test"
 
 if ! command -v quickshell >/dev/null 2>&1; then
   pass "quickshell not installed; skipping QML contract test"