command/spawn-tagmask: apply globally

Currently the spawn-tagmask applies to the currently focused output.
This however means that it is lost if the monitor is unplugged and makes
it hard to set for all outputs.

Change this to make the command apply to all outputs.

This is a breaking change.

river/command/tags.zig

@@ -39,14 +39,13 @@ pub fn setFocusedTags(
     }
 }
 
-/// Set the spawn tagmask
 pub fn spawnTagmask(
-    seat: *Seat,
+    _: *Seat,
     args: []const [:0]const u8,
     out: *?[]const u8,
 ) Error!void {
     const tags = try parseTags(args, out);
-    seat.focused_output.spawn_tagmask = tags;
+    server.config.spawn_tagmask = tags;
 }
 
 /// Set the tags of the focused view.