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/pki/station_config_filesystem.hpp

@@ -0,0 +1,34 @@
+#pragma once
+
+#include "filesystem.hpp"
+#include "station_config.hpp"
+
+namespace vanetza
+{
+namespace pki
+{
+
+class StationConfigurationFilesystem : public StationConfiguration
+{
+public:
+    StationConfigurationFilesystem(const std::filesystem::path&);
+
+    std::string get_canonical_identifier() const override;
+    void set_canonical_identifier(const std::string&) override;
+
+    boost::optional<HashedId8> get_ec_identifier() const override;
+    void set_ec_identifier(const HashedId8&) override;
+
+    boost::optional<HashedId8> get_root_ca() const override;
+    void set_root_ca(const HashedId8&) override;
+
+protected:
+    boost::optional<HashedId8> get_hid8(const std::filesystem::path&) const;
+    void set_hid8(const std::filesystem::path&, const HashedId8&);
+
+private:
+    std::filesystem::path m_root;
+};
+
+} // namespace pki
+} // namespace vanetza