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/vanetza/geonet/CMakeLists.txt

@@ -0,0 +1,48 @@
+set(CXX_SOURCES
+    address.cpp
+    areas.cpp
+    basic_header.cpp
+    beacon_header.cpp
+    cbf_packet_buffer.cpp
+    cbf_counter.cpp
+    cbf_packet_identifier.cpp
+    cbr_aggregator.cpp
+    common_header.cpp
+    data_confirm.cpp
+    data_request.cpp
+    dcc_field.cpp
+    dcc_information_sharing.cpp
+    dcc_mco_field.cpp
+    duplicate_packet_list.cpp
+    gbc_gac_header.cpp
+    gbc_header.cpp
+    gbc_memory.cpp
+    header_type.cpp
+    header_variant.cpp
+    indication_context.cpp
+    mib.cpp
+    sequence_number.cpp
+    lifetime.cpp
+    location_table.cpp
+    next_hop.cpp
+    packet_buffer.cpp
+    parser.cpp
+    pdu.cpp
+    pdu_conversion.cpp
+    position_updater.cpp
+    position_vector.cpp
+    repeater.cpp
+    router.cpp
+    secured_pdu.cpp
+    shb_header.cpp
+    timestamp.cpp
+    traffic_class.cpp
+    tsb_header.cpp
+    variant_pdu.cpp
+)
+
+add_vanetza_component(geonet ${CXX_SOURCES})
+target_link_libraries(geonet PUBLIC Boost::date_time)
+target_link_libraries(geonet PUBLIC dcc geodesy net security)
+
+add_test_subdirectory(tests)