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/server/web/static/app.css

@@ -34,7 +34,7 @@ header.topbar nav a:hover { color: var(--text); }
 h1 { font-size: 22px; margin: 0 0 18px; }
 h2 { font-size: 17px; margin: 0 0 14px; }
 label { display: block; margin: 12px 0 4px; color: var(--muted); font-size: 13px; }
-input[type=text], input[type=password] {
+input[type=text], input[type=password], select {
   width: 100%; padding: 10px 12px; border-radius: 8px;
   border: 1px solid var(--border); background: #0c0f13; color: var(--text); font-size: 14px;
 }