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

test/test_version/test_version.cpp

@@ -14,9 +14,16 @@ void test_product_name() {
     TEST_ASSERT_EQUAL_STRING("roro9stack", roro::kProductName);
 }
 
+void test_uname_has_name_version_and_architecture() {
+    std::string expected = std::string("roro9stack ") + roro::versionString() + " " + roro::architectureString();
+    TEST_ASSERT_EQUAL_STRING(expected.c_str(), roro::unameString().c_str());
+    TEST_ASSERT_TRUE(std::strlen(roro::architectureString()) > 0);
+}
+
 int main() {
     UNITY_BEGIN();
     RUN_TEST(test_version_is_never_empty);
     RUN_TEST(test_product_name);
+    RUN_TEST(test_uname_has_name_version_and_architecture);
     return UNITY_END();
 }