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/client.go

@@ -120,6 +120,7 @@ func (a *Agent) enroll(ctx context.Context) error {
 		OS:       runtime.GOOS,
 		Arch:     runtime.GOARCH,
 		Version:  Version,
+		User:     currentUser(),
 	})
 	req, _ := http.NewRequestWithContext(ctx, http.MethodPost, a.cfg.Host+"/api/agent/enroll", bytes.NewReader(body))
 	req.Header.Set("X-Enroll-Secret", a.cfg.EnrollSecret)
@@ -145,11 +146,12 @@ func (a *Agent) enroll(ctx context.Context) error {
 func (a *Agent) pollOnce(ctx context.Context) error {
 	req, _ := http.NewRequestWithContext(ctx, http.MethodGet, a.cfg.Host+"/api/agent/poll", nil)
 	a.authHeaders(req)
-	// Report the version occasionally (not every poll), so the panel can flag
-	// outdated agents without extra traffic.
+	// Report the version and our OS user occasionally (not every poll), so the
+	// panel can flag outdated agents without extra traffic.
 	a.pollCount++
 	if a.pollCount%20 == 1 {
 		req.Header.Set("X-Agent-Version", Version)
+		req.Header.Set("X-Agent-User", currentUser())
 	}
 	resp, err := a.http.Do(req)
 	if err != nil {
@@ -169,7 +171,7 @@ func (a *Agent) pollOnce(ctx context.Context) error {
 	// Dispatch in the background so we keep polling for more work.
 	switch msg.Type {
 	case proto.CtrlOpenTerminal:
-		go a.runTerminal(ctx, msg.SessionID)
+		go a.runTerminal(ctx, msg.SessionID, msg.User)
 	case proto.CtrlOpenForward:
 		go a.runForward(ctx, msg.SessionID, msg.Port)
 	case proto.CtrlTask: