Ties systemd units to graphical-session.target

- wayland-instance template target was a mistake.
  Systemd does not support simultaneous same user session, so stop
  trying to go against that.
- Only start systemd units in Wayland environments.

foot-server.service.in

@@ -1,13 +1,13 @@
 [Service]
 ExecStart=@bindir@/foot --server=3
-Environment=WAYLAND_DISPLAY=%i
 UnsetEnvironment=LISTEN_PID LISTEN_FDS LISTEN_FDNAMES
 NonBlocking=true
 
 [Unit]
 Requires=%N.socket
-Description=Foot terminal server mode for WAYLAND_DISPLAY=%i
+Description=Foot terminal server mode
 Documentation=man:foot(1)
+PartOf=graphical-session.target
 
 [Install]
-WantedBy=wayland-instance@.target
+WantedBy=graphical-session.target

foot-server.socket

@@ -0,0 +1,9 @@
+[Socket]
+ListenStream=%t/foot.sock
+
+[Unit]
+PartOf=graphical-session.target
+ConditionEnvironment=WAYLAND_DISPLAY
+
+[Install]
+WantedBy=graphical-session.target

foot-server@.socket

@@ -1,5 +0,0 @@
-[Socket]
-ListenStream=%t/foot-%i.sock
-
-[Install]
-WantedBy=wayland-instance@.target

meson.build

@@ -329,13 +329,13 @@ if systemd.found() or custom_systemd_units_dir != ''
 
   configure_file(
     configuration: configuration,
-    input: 'foot-server@.service.in',
+    input: 'foot-server.service.in',
     output: '@BASENAME@',
     install_dir: systemd_units_dir
     )
 
   install_data(
-    'foot-server@.socket',
+    'foot-server.socket',
     install_dir: systemd_units_dir)
 endif