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/main.cpp

@@ -0,0 +1,18 @@
+#include "options.hpp"
+#include <iostream>
+
+int main(int argc, const char** argv)
+{
+    try {
+        std::unique_ptr<Command> command = parse_options(argc, argv);
+
+        if (!command) {
+            return 1;
+        }
+
+        return command->execute();
+    } catch (const std::exception& e) {
+        std::cerr << e.what() << std::endl;
+        return 1;
+    }
+}