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/docs/idf/evidence/radio-pair-01/result.json

@@ -0,0 +1,18 @@
+{
+  "kind": "radio-integration",
+  "dut": "COM20",
+  "receiver": "COM11",
+  "channel": 180,
+  "status": "pass",
+  "captures": [
+    {
+      "rssi_dbm": -46,
+      "device_timestamp_us": 48779796,
+      "trailing_bytes": "00009900",
+      "exact_match": true
+    }
+  ],
+  "cleanup_errors": [],
+  "receive_only_tx_rejected": true,
+  "submission_accepted": true
+}