fix(agent/windows): named pipe Tailscale + hideWindow + logs

- Use Windows named pipe \.\pipe\studioe5-tailscaled instead of Unix socket
- Apply hideWindow to all child processes (tailscale, podman, docker, browser)
- Redirect agent logs to <data-dir>/agent.log and tailscaled logs to tailscaled.log
- Fix double tailscale/ tailscale dir path in startTailscaleAndReport
- Remove --operator=root on Windows
- Bump agent version to 0.3.1

agent/exec_unix.go

@@ -0,0 +1,8 @@
+//go:build !windows
+
+package main
+
+import "os/exec"
+
+// hideWindow is a no-op on non-Windows platforms.
+func hideWindow(cmd *exec.Cmd) {}