start syncthing on load with launchd and improve dock/spaces defaults

nix/system/worktop/darwin-configuration.nix

@@ -51,6 +51,15 @@
     ''
   );
 
+  launchd.user.agents.syncthing = {
+    path = [ pkgs.syncthing ];
+    command = "syncthing serve";
+    serviceConfig = {
+      ProcessType = "Background";
+      KeepAlive = true;
+    };
+  };
+
   system.keyboard = {
     enableKeyMapping = true;
     remapCapsLockToEscape = true;
@@ -58,6 +67,12 @@
 
   system.defaults = {
     finder.AppleShowAllExtensions = true;
+
+    dock = {
+      autohide = true;
+      mru-spaces = false;
+      showhidden = true;
+    };
   };
 
   # Used for backwards compatibility, please read the changelog before changing.