Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/tools/certify/commands/show-certificate.hpp

@@ -0,0 +1,16 @@
+#ifndef CERTIFY_COMMANDS_SHOW_CERTIFICATE_HPP
+#define CERTIFY_COMMANDS_SHOW_CERTIFICATE_HPP
+
+#include "command.hpp"
+
+class ShowCertificateCommand : public Command
+{
+public:
+    bool parse(const std::vector<std::string>&) override;
+    int execute() override;
+
+private:
+    std::string certificate_path;
+};
+
+#endif /* CERTIFY_COMMANDS_SHOW_CERTIFICATE_HPP */