chore: check we are in terminal before creating one

I tried to run `node-launchpad` in a headless VM and it said it couldn't find a terminal. We don't
need to find a terminal if we are already running in one, so the check here is changed slightly.

We will probably want to reconfigure the elevated privilege to be a separate thing from configuring
a terminal, but on Windows this will be a bit more complex and will better be done as a separate
piece of work.

node-launchpad/src/bin/tui/main.rs

@@ -58,15 +58,11 @@ fn is_running_in_terminal() -> bool {
 
 #[tokio::main]
 async fn main() -> Result<()> {
-    // now launch the terminal
-    let terminal_type = terminal::detect_and_setup_terminal()?;
-
     if !is_running_in_terminal() {
+        // If we weren't already running in a terminal, this process returns early, having spawned
+        // a new process that launches a terminal.
+        let terminal_type = terminal::detect_and_setup_terminal()?;
         terminal::launch_terminal(&terminal_type)?;
-
-        // early return for _this_ process.
-        // The spawned process will be sudo'd and run in the terminal,
-        // taking over stdout/stderr/stdin.
         return Ok(());
     }