Shell: tls, ntp and netstat (#90)

The rest of the issue's list. tls makes a handshake that checks nothing,
then says the certificate in words: who it is for, who signed it, until
when, and whether this device's roots and the name asked for accept it,
with the reason when they don't. ntp compares a time server's clock with
the device's. netstat lists what listens and what is connected.

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

src/main.cpp

@@ -231,6 +231,7 @@ void setup() {
     apps->registerApp({"shell", "Shell", false, new ShellApp(shellRun, shellProbe, shellList, shellCount, helpText(), *apps)});
     // Leaving the foreground App makes it save: a note being typed, when the device is powered off.
     power->beforePowerOff = []() { apps->home(); };
+    netTools.ntpServer = []() { return settings.getString(Setting::Ntp1); };
     // A long note being rewritten (issue #47): the editor waits for the card, so it draws from there.
     NoteEditor::onProgress = [](const std::string& name, int percent) { screen.renderUpdate("Saving", name, percent); };
     apps->registerApp({"system", "System", false,
@@ -677,7 +678,8 @@ static const char* const kHelp =
     "sd card | sd list | cat <path> | log <text> | burst | sound on|off | short | normal\n"
     "Irc | Wifi | Gnss | Gemini | Lora | Storage | Notes | Shell | System | Settings   open that App: a capital letter is an App, not a command\n"
     "ping <host> [count] [size] | nslookup <name> [server] | port <host> <port> | traceroute <host> | cancel   is it there, does its name resolve, is its port open, which way; one at a time\n"
-    "ifconfig | arp    the interfaces (Wi-Fi and the VPN), their addresses, the default route and the DNS servers; the neighbours heard\n"
+    "tls <host> [port] | ntp [server]   a TLS handshake: who the certificate is for, by whom, until when, and whether this device trusts it; a time server's clock against this one\n"
+    "ifconfig | arp | netstat   the interfaces (Wi-Fi and the VPN), their addresses, the default route and the DNS servers; the neighbours heard; what listens and what is connected\n"
     "vpn status | vpn up [seconds] | vpn down | vpn import [path] | vpn forget | vpn auto on|off   the WireGuard tunnel (Settings > VPN); import reads /vpn/wg0.conf; with seconds, it goes down by itself\n"
     "debug status | debug off [seconds]   the Debug Console over Wi-Fi (Settings > Debug Console); with seconds, it comes back\n"
     "debug on | debug token <16 to 64 characters> | debug token new   (USB serial only) switch it on, set its token\n"