feat: terminal as a chosen OS user, create users from the panel (0.0.2)

- agent reports the OS user it runs as (enroll + poll header)
- per-machine terminal user on the edit page; defaults to the agent's own user (root on Linux)
- create a new user from the panel: name, password, optional sudo group
- show the reason in the terminal when a shell fails to start
- bump version to 0.0.2

internal/agent/session.go

@@ -15,14 +15,17 @@ import (
 )
 
 // runTerminal spawns a PTY and bridges it to the session.
-func (a *Agent) runTerminal(parent context.Context, sid string) {
-	term, err := StartPTY()
+// user is the OS user to run the shell as ("" = the agent's own user).
+func (a *Agent) runTerminal(parent context.Context, sid, user string) {
+	term, err := StartPTY(user)
 	if err != nil {
 		log.Printf("term %s: start pty: %v", sid, err)
+		// Show the reason in the browser terminal before closing it.
+		a.postOut(context.Background(), sid, proto.OutMessage{Data: b64.EncodeToString([]byte("lpra: " + err.Error() + "\r\n"))})
 		a.postOut(context.Background(), sid, proto.OutMessage{Exit: true})
 		return
 	}
-	log.Printf("term %s: shell started", sid)
+	log.Printf("term %s: shell started (user %q)", sid, user)
 	a.bridgeStream(parent, sid, term, term.Resize)
 	log.Printf("term %s: ended", sid)
 }