Remove the IPC socket of each shell a test starts (#13443)

* Answer the Elsewhen panel over the shell's IPC socket

The Elsewhen panel arrived with a plain IpcHandler, so omarchy-shell
reached it only through the slower qs ipc fallback, and the test that
every first-party handler registers as ShellIpc failed on quattro.

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

* Remove the IPC socket of each shell a test starts

The runtime smoke and screenshot sanity tests start the real shell from a
temporary copy and kill it, which leaves its IPC socket behind in
XDG_RUNTIME_DIR. A session that runs the suite a few times collected
dozens of them.

base-test.sh gains shell_ipc_socket, which derives a shell's socket as
omarchy-shell does, and both tests remove theirs in cleanup. The socket
test derives its fixture's socket through it too, so the helper cannot
drift from omarchy-shell.

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

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/shell.d/base-test.sh

@@ -27,6 +27,15 @@ fail() {
   exit 1
 }
 
+# The IPC socket a shell running an OMARCHY_PATH's config on this display
+# serves, derived as omarchy-shell derives it. A test that starts the real
+# shell removes it afterwards: killing the shell leaves the file behind.
+shell_ipc_socket() {
+  local id
+  id=$(printf '%s\n%s' "$1/shell" "${WAYLAND_DISPLAY:-}" | md5sum)
+  printf '%s/omarchy-shell-%s.sock\n' "${XDG_RUNTIME_DIR:-/run/user/$UID}" "${id:0:16}"
+}
+
 require_command() {
   local command="$1"