Fix rbw-agent launching from systemd services

The rbw unlock systemd services were failing to launch the rbw-agent
daemon due to two issues:

1. Missing RBW_AGENT environment variable - rbw looks for this variable
   to locate the agent binary, falling back to PATH lookup. Systemd
   user services have minimal environments without the necessary PATH.

2. Default KillMode=control-group - when the oneshot service completed,
   systemd was killing all processes in the cgroup including the
   daemonized agent.

Fixed by:
- Setting RBW_AGENT environment variable to explicit agent binary path
- Using KillMode=process to only kill the main process, allowing the
  spawned agent daemon to persist after service completion

home/roles/desktop/default.nix

@@ -90,7 +90,11 @@ in
       Service = {
         Type = "oneshot";
         ExecStart = "${pkgs.rbw}/bin/rbw unlock";
-        Environment = "PATH=${pkgs.rbw}/bin:/run/current-system/sw/bin";
+        Environment = "RBW_AGENT=${pkgs.rbw}/bin/rbw-agent";
+        # KillMode = "process" prevents systemd from killing the rbw-agent daemon
+        # when this oneshot service completes. The agent is spawned by rbw unlock
+        # and needs to persist after the service exits.
+        KillMode = "process";
       };
       Install = {
         WantedBy = [ "graphical-session.target" ];
@@ -105,7 +109,11 @@ in
       Service = {
         Type = "oneshot";
         ExecStart = "${pkgs.rbw}/bin/rbw unlock";
-        Environment = "PATH=${pkgs.rbw}/bin:/run/current-system/sw/bin";
+        Environment = "RBW_AGENT=${pkgs.rbw}/bin/rbw-agent";
+        # KillMode = "process" prevents systemd from killing the rbw-agent daemon
+        # when this oneshot service completes. The agent is spawned by rbw unlock
+        # and needs to persist after the service exits.
+        KillMode = "process";
       };
       Install = {
         WantedBy = [ "suspend.target" ];