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/version/src/version.cpp

@@ -8,8 +8,26 @@
 #define RORO_VERSION "unknown"
 #endif
 
+#if __has_include("sdkconfig.h")
+#include "sdkconfig.h"
+#endif
+
 namespace roro {
 
 const char* versionString() { return RORO_VERSION; }
 
+const char* architectureString() {
+#if defined(CONFIG_IDF_TARGET_ESP32S3)
+    return "xtensa-lx7 esp32s3";
+#elif defined(CONFIG_IDF_TARGET_ESP32)
+    return "xtensa-lx6 esp32";
+#elif defined(CONFIG_IDF_TARGET)
+    return CONFIG_IDF_TARGET;
+#else
+    return "host";
+#endif
+}
+
+std::string unameString() { return std::string(kProductName) + " " + versionString() + " " + architectureString(); }
+
 }  // namespace roro