Drive the ESP32-C5 station over USB or BLE, send CAM or VAM, signed or not

The app now speaks the station-link protocol of the new obu-firmware.
Esp32Link picks the transport from Settings (UsbSerialTransport or the new
BleLinkTransport), tells the previous firmware from the new one by its
heartbeat, and runs the session: STATION_CONFIGURE with the current pseudonym
MAC (which also starts the board's radio), CREDENTIALS_PROVISION of the
bundled demo chain when the board has no ticket, then per message a
POTI_UPDATE and a BTP_DATA_REQUEST. Received messages still arrive as
V2X_RX frames, so the receive side is unchanged. A board on the previous
firmware keeps working for CAM over USB.

Settings > Connection > ESP32-C5: link USB-C or Bluetooth, transmit CAM or
VAM, "Sign outgoing messages" (on by default). The connection card, top bar
and dashboard show the link in use, the pairing passkey and signing counters.

- VAM: VamUperCodec (TS 103 300-3 V2.3.1, bytes checked against asn1tools)
  and VamGenerationRules (clause 6.4, Tables 16/17).
- BLE: the firmware's GATT layout (service 0000C175-...), MTU 517, pairing
  and encryption settled before any other operation (short timeouts during
  pairing made it loop), backoff between attempts, reasons on the card.
- Clock: a PoTi goes to the board once per new fix and never moves the
  board's clock backwards except for a real correction (>= 60 s); stale and
  wobbling fix times made the board answer time_regression and restart its
  stack every few seconds. GnssTimeSource keeps the last measured phone-clock
  error while GNSS time drops out indoors: the bench phone is 14 minutes fast,
  and falling back to it made every transmitted timestamp jump by that much.
- assets/demo-chain.vcr: throwaway, not EU-registered demo chain generated
  2026-09-23 (AT B80B49387A4C12EB, psid 36 and 638). Its private key ships
  with the app on purpose; receivers verifying against the EU trust list
  drop what it signs.
- Bluetooth permissions requested at start-up on Android 12+.

StationLinkTest pins the codec to bytes from the colleague's Python
implementation (microbu_link/messages.py). 103 unit tests pass.

app/src/main/AndroidManifest.xml

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
-<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools">
 
     <!-- Networking (MQTT / tile downloads) -->
     <uses-permission android:name="android.permission.INTERNET" />
@@ -10,6 +11,15 @@
 
     <!-- Location -->
     <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
+    <!-- BLE link to the ESP32-C5 (BleLinkTransport). Android 12+ asks for scan/connect at runtime;
+         older versions use the legacy pair plus location, which is requested anyway. -->
+    <uses-permission android:name="android.permission.BLUETOOTH" android:maxSdkVersion="30" />
+    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" android:maxSdkVersion="30" />
+    <uses-permission android:name="android.permission.BLUETOOTH_SCAN"
+        android:usesPermissionFlags="neverForLocation"
+        tools:targetApi="s" />
+    <uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
+    <uses-feature android:name="android.hardware.bluetooth_le" android:required="false" />
     <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
 
     <!-- Phase A: foreground service (trip recording) -->