Use cosmic-greeter as the greetd user

cosmic-greeter.toml

@@ -3,4 +3,4 @@ vt = "1"
 
 [default_session]
 command = "cage -s -- cosmic-greeter"
-user = "greeter"
+user = "cosmic-greeter"

debian/postinst

@@ -0,0 +1,2 @@
+#!/bin/bash
+useradd --groups video --no-create-home --system cosmic-greeter

src/main.rs

@@ -19,7 +19,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
 
     match pwd::Passwd::current_user() {
         Some(current_user) => match current_user.name.as_str() {
-            "greeter" => greeter::main(),
+            "cosmic-greeter" => greeter::main(),
             _ => locker::main(current_user),
         },
         _ => Err("failed to determine current user".into()),