Sign ITS messages on the ESP32-C5 with vanetza-idf, over USB or BLE

obu-firmware is now a port of the colleague's standalone VRU station
(microbu-esp32c5/firmware, kept beside this repository and gitignored): the
vanetza-idf C-ITS stack with the TS 103 097 security entity, credentials in
NVS, the station-link v1 protocol over the native USB port (frame type 0x10
in the existing 0xAA55 framing) and over a BLE GATT peripheral, and its
ITS-G5 radio adapter. The phone still builds CAM and VAM; the board adds
GeoNetworking/BTP and signs with the provisioned authorization ticket. The
private key never leaves the board. Builds with ESP-IDF 6.0.2 only, which
vanetza-idf pins for the radio's private driver ABI. The previous C firmware
stays on disk unbuilt; a full-flash backup of the bench board is kept in
firmware-backups/ (gitignored).

Changed against the colleague's firmware, marked MicrOBU: in the sources:
- Reception unchanged for the app. vanetza-idf drops what it cannot verify
  (unsigned traffic, every RSU), so each captured frame also goes through the
  previous gn_unwrap.c and reaches the phone as link opcode V2X_RX (0x85),
  whose body is the old SERIAL_MSG_V2X_RX payload.
- Unsigned transmission still possible, with the previous geonet.c header;
  the phone chooses per message.
- Console on UART0 (CH343 port); the native USB port carries only link frames.
- BLE advertising pauses while the USB link is in use: BLE and ITS-G5 share
  one RF front end.
- NVS 80 KB (app at 0x20000). At 24 KB, with Wi-Fi settings the previous
  firmware left behind, the BLE bond could not be stored and the phone had to
  pair on every connection.
- Bench fixes: the radio queue is drained before the first PoTi (no RX and
  ~177 queue drops before); the station loop waited pdMS_TO_TICKS(5) = 0
  ticks at 100 Hz and starved the idle task; the 2.4 KB RX capture buffer is
  off the Wi-Fi task stack; BLE notifications longer than the MTU are dropped
  instead of cut short, MTU 517; serial writes are skipped with no USB host.
- Manual country policy and TX-power read-back from the previous radio setup;
  logs for BLE encryption changes and the number of stored bonds.

Verified on the bench board (COM3) with the phone over USB and BLE: CAM and
VAM, signed and unsigned, go out; reception of the sim car and the RSU's
CAM/SPATEM/MAPEM continues; the board survives app restarts and reconnects.
See docs/06-signed-its-vam-ble.md.

obu-firmware/sdkconfig.defaults

@@ -1 +1,54 @@
+# obu-firmware defaults (ESP32-C5, ESP-IDF 6.0.2). Based on microbu-esp32c5/firmware/sdkconfig.defaults;
+# the differences for this board are marked "MicrOBU:".
 CONFIG_IDF_TARGET="esp32c5"
+CONFIG_COMPILER_CXX_EXCEPTIONS=y
+CONFIG_COMPILER_CXX_RTTI=y
+CONFIG_COMPILER_OPTIMIZATION_SIZE=y
+CONFIG_ESP_MAIN_TASK_STACK_SIZE=8192
+# MicrOBU: the production board has 16 MB of flash (esptool reports it); the partition table
+# only uses the first 4 MB.
+CONFIG_ESPTOOLPY_FLASHSIZE_16MB=y
+CONFIG_PARTITION_TABLE_CUSTOM=y
+CONFIG_PARTITION_TABLE_CUSTOM_FILENAME="partitions.csv"
+# Network profile: BTP + GeoNetworking, no facilities codecs (the phone builds CAM/VAM)
+CONFIG_VANETZA_IDF_PROFILE_NETWORK=y
+CONFIG_VANETZA_IDF_SECURITY=y
+CONFIG_VANETZA_IDF_SECURITY_VERIFY=y
+CONFIG_VANETZA_IDF_NVS_CREDENTIALS=y
+CONFIG_VANETZA_IDF_PKI=n
+CONFIG_VANETZA_IDF_HIL=n
+CONFIG_VANETZA_IDF_RADIO_C5=y
+CONFIG_ESP_WIFI_STATIC_RX_BUFFER_NUM=6
+CONFIG_ESP_WIFI_DYNAMIC_RX_BUFFER_NUM=16
+CONFIG_ESP_WIFI_DYNAMIC_TX_BUFFER_NUM=16
+CONFIG_ESP_WIFI_MGMT_SBUF_NUM=16
+# MicrOBU: the console and ESP_LOG stay on UART0, i.e. the CH343 bridge port (COM3 on the bench),
+# exactly as in the previous firmware. The native USB Serial/JTAG port belongs to the phone and
+# carries only station-link frames. The colleague's board has only the native port and routes the
+# console there instead.
+CONFIG_ESP_CONSOLE_UART_DEFAULT=y
+CONFIG_ESP_CONSOLE_SECONDARY_NONE=y
+CONFIG_ESP_PANIC_HANDLER_IRAM=y
+CONFIG_LOG_DEFAULT_LEVEL_INFO=y
+CONFIG_LOG_COLORS=n
+# MicrOBU: 20 dBm ceiling, as the previous firmware (the phone configures 20).
+CONFIG_ESP_PHY_MAX_WIFI_TX_POWER=20
+# Station-internal BLE GATT link: NimBLE, maximum ATT value, persistent bonds.
+CONFIG_BT_ENABLED=y
+CONFIG_BT_BLUEDROID_ENABLED=n
+CONFIG_BT_NIMBLE_ENABLED=y
+CONFIG_BT_NIMBLE_ATT_PREFERRED_MTU=517
+CONFIG_BT_NIMBLE_SM_SC=y
+CONFIG_BT_NIMBLE_NVS_PERSIST=y
+CONFIG_BT_NIMBLE_MAX_CONNECTIONS=1
+CONFIG_BT_NIMBLE_MAX_BONDS=1
+CONFIG_BT_NIMBLE_MAX_CCCDS=8
+CONFIG_BT_NIMBLE_MSYS_1_BLOCK_COUNT=12
+CONFIG_BT_NIMBLE_MSYS_2_BLOCK_COUNT=12
+CONFIG_BT_NIMBLE_ROLE_CENTRAL=n
+CONFIG_BT_NIMBLE_ROLE_OBSERVER=n
+# Hardware ECDSA/ECC/SHA
+CONFIG_MBEDTLS_HARDWARE_ECC=y
+CONFIG_MBEDTLS_HARDWARE_ECDSA_VERIFY=y
+CONFIG_MBEDTLS_HARDWARE_SHA=y
+CONFIG_MBEDTLS_HARDWARE_AES=n