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FLASHING.md says how to take a newer version of the colleague's tree (copy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/.gitignore

@@ -0,0 +1,43 @@
+# --- ESP-IDF build output ---
+firmware/build/
+firmware/build-*/
+firmware/managed_components/
+firmware/.cache/
+firmware/.vscode/
+firmware/sdkconfig
+firmware/sdkconfig.old
+firmware/*.log
+firmware/rf_characterization_output/
+
+# --- Secrets: never commit real private key material ---
+# (this repo only ever ships the disposable, non-registered demo chain)
+*.vkey
+*.ekey
+private/
+*_private_encrypted.pem
+*_RCA_NEW_*/
+
+# --- PKI reference-generator: regenerate locally, do not commit ---
+# (vendored Rust crates for the offline/deterministic c-its build path; see
+# pki/uml-l0-rca/reference-generator/README.md to rebuild with `cargo vendor`)
+pki/uml-l0-rca/reference-generator/vendor/
+pki/uml-l0-rca/reference-generator/_build_cits/
+pki/uml-l0-rca/reference-generator/_cargo_vendor/
+
+# --- Python ---
+__pycache__/
+*.pyc
+*.egg-info/
+.venv/
+venv/
+
+# --- v2x2map bridge local artifacts ---
+tools/v2x2map-0.3.0/bridge/recordings/
+tools/v2x2map-0.3.0/bridge/dist/
+tools/v2x2map-0.3.0/bridge/build/
+*.pcap
+
+# --- OS / editor ---
+.DS_Store
+Thumbs.db
+*.swp