Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/external/vanetza-idf/tools/certify-pqc/certificate_builder.hpp

@@ -0,0 +1,67 @@
+#pragma once
+
+#include <vanetza/common/clock.hpp>
+#include <vanetza/common/its_aid.hpp>
+#include <vanetza/security/ecdsa256.hpp>
+#include <vanetza/security/pqc/fndsa512.hpp>
+#include <vanetza/security/v3/certificate.hpp>
+#include <string>
+#include <vector>
+
+namespace vanetza
+{
+namespace security
+{
+
+class Backend;
+
+namespace pqc
+{
+namespace certificate_builder
+{
+
+struct CertificateParameters
+{
+    std::string subject_name;
+    int validity_days = 1;
+    std::vector<ItsAid> application_ids;
+};
+
+v3::Certificate build_ecc_root_certificate(
+    ::vanetza::security::Backend&, const ecdsa256::KeyPair&,
+    const CertificateParameters&, Clock::time_point now);
+
+v3::Certificate build_hybrid_root_certificate(
+    ::vanetza::security::Backend&, Backend&, const ecdsa256::KeyPair&, const KeyPair&,
+    const CertificateParameters&, Clock::time_point now);
+
+v3::Certificate build_ecc_authorization_authority_certificate(
+    ::vanetza::security::Backend&, const ecdsa256::KeyPair& issuer_key,
+    const v3::Certificate& issuer_certificate,
+    const ecdsa256::PublicKey& subject_key,
+    const CertificateParameters&, Clock::time_point now);
+
+v3::Certificate build_hybrid_authorization_authority_certificate(
+    ::vanetza::security::Backend&, Backend&,
+    const ecdsa256::KeyPair& issuer_key, const PrivateKey& issuer_pqc_key,
+    const v3::Certificate& issuer_certificate,
+    const ecdsa256::PublicKey& subject_key, const PublicKey& subject_pqc_key,
+    const CertificateParameters&, Clock::time_point now);
+
+v3::Certificate build_ecc_authorization_ticket(
+    ::vanetza::security::Backend&, const ecdsa256::KeyPair& issuer_key,
+    const v3::Certificate& issuer_certificate,
+    const ecdsa256::PublicKey& subject_key,
+    const CertificateParameters&, Clock::time_point now);
+
+v3::Certificate build_hybrid_authorization_ticket(
+    ::vanetza::security::Backend&, Backend&,
+    const ecdsa256::KeyPair& issuer_key, const PrivateKey& issuer_pqc_key,
+    const v3::Certificate& issuer_certificate,
+    const ecdsa256::PublicKey& subject_key,
+    const CertificateParameters&, Clock::time_point now);
+
+} // namespace certificate_builder
+} // namespace pqc
+} // namespace security
+} // namespace vanetza