Shell: ping, nslookup, port, traceroute, ifconfig and arp (#90)

Network troubleshooting from the device itself, in the Shell and over both
consoles. ping, nslookup, port and traceroute each run on a task of their
own and print as they go, to the console that asked; one at a time, and
`cancel` stops it. ifconfig and arp answer at once: the interfaces (Wi-Fi
and the VPN), which is the default route, the DNS servers, the neighbours.

nslookup asks a DNS server itself, so it can say which server answered and
in how long, and ask another. A sized ping finds what a tunnel really
carries.

With a how-to, "When the network doesn't work", and the rest of the docs.
tls, ntp and netstat from the issue's list are not in this.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/services/net_tools.h

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <atomic>
+#include <string>
+
+#include "platform/console.h"
+
+namespace roro {
+
+// The network troubleshooting commands (issue #90): ping, nslookup, port, traceroute, ifconfig,
+// arp. The first four take time, so each runs on a task of its own and prints its lines as they
+// come, to the console that asked; one at a time, and `cancel` stops it. The other two answer at
+// once. The packets and their meaning are lib/net/src/net_probe.h, which is host-tested.
+class NetTools {
+   public:
+    // True if `line` was one of its commands (answered, started, or refused with a reason).
+    bool command(const std::string& line);
+    bool busy() const { return busy_; }
+    void cancel() { stop_ = true; }
+
+   private:
+    struct Job;
+    void start(Job* job);
+    static void task(void* arg);
+
+    std::atomic<bool> busy_{false}, stop_{false};
+};
+
+}  // namespace roro