Add uname, /uname and scp (key or masked password) in the Shell

- uname in the console and /uname in IRC: the firmware, its version and the chip
- scp: one file between the card and a trusted server, over SSH, with the
  device's key or a password asked (masked) in the Shell
- shared libssh helpers in src/platform/libssh_util
- README, user guide, command reference and a how-to updated

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0162FokPdvY2KsS4NBfwyWPk

lib/term/src/scp_args.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <string>
+
+#include "ssh_hosts.h"
+
+namespace roro::term {
+
+// What `scp` was asked: one file to the card from a server, or from the card to a server.
+//   scp [-f] [-P port] /notes/a.txt user@host:path     (upload)
+//   scp [-f] [-P port] user@host:path /notes/a.txt     (download; a destination ending in / gets the remote file's name)
+// The card's paths start with a slash; the server's are the server's own (relative ones start at the home folder).
+struct ScpArgs {
+    bool upload = false;
+    bool replace = false;  // -f: a download may replace a file on the card
+    SshTarget target;
+    std::string local, remote;
+};
+
+// "" or what is wrong with it.
+std::string parseScp(const std::string& args, ScpArgs& out);
+
+}  // namespace roro::term