Fix UPER encoding of CurvatureCalculationMode; verified on hardware

CurvatureCalculationMode is the one extensible ENUMERATED in CAM:
  ENUMERATED {yawRateUsed(0), yawRateNotUsed(1), unavailable(2), ...}
UPER encodes an extensible ENUMERATED as an extension bit followed by the root
index - 1 + 2 = 3 bits. All three of our encoders wrote only the 2-bit index,
shifting yawRate and the entire low-frequency container one bit early for any
standards-compliant receiver.

It went unnoticed because every end of this project shared the mistake: the
Kotlin codec was ported bit-for-bit from cam.c, so phone and ESP32 agreed
perfectly with each other and with nothing else. Confirmed against the ETSI
ASN.1 in the C-ITS-Parser checkout, where rasn marks this type - and only this
type - #[non_exhaustive].

Fixed in all three copies of the encoder (app CamUperCodec.kt,
obu-firmware/main/cam.c, obu-cam-transmistter/main/cam.c) plus the decoder,
which now rejects rather than misreads a set extension bit. Frame size is
unchanged at 43 bytes. Transmitter reflashed and the phone decodes its CAMs.

Also in this change:

- serial_link: skip send_frame entirely when no USB host is attached, and raise
  the tx mutex timeout above the worst-case hold. With the phone unplugged every
  write blocked its full timeout while holding the lock, so forwarded CAM_RX
  traffic starved the 1 Hz heartbeat - observed as "tx mutex timeout, dropping
  frame" on the console, and it would have tripped the phone's link watchdog.
  Verified gone on hardware.
- Log decoded and failed CAMs in CamUseCaseRepository. "The app shows nothing"
  had two indistinguishable causes; a silent `?: return` made this bug much
  harder to find than it needed to be.
- Remove the ESP32 send-only/send-and-receive toggle. Reception can't be
  disabled in firmware (raw TX only works while promiscuous), so it was an
  app-side filter pretending to be a radio control.
- V2X monitor follows the serial link state on the ESP32 path instead of MQTT,
  which is permanently disconnected there; CAM intake is gated on the link being
  up, and engine state is cleared when it drops.
- About screen: 0.5.0, Phase 03.
- Track obu-cam-transmistter, the bench CAM transmitter. Its cam.c is compiled
  (unlike obu-firmware's reference copy) and must stay bit-identical to the other
  two - this commit is what that coupling costs when it's broken.
- Document the two-toolchain split: this project builds on IDF 5.5.4, obu-firmware
  on the pinned 6.1. Exporting both in one shell fails confusingly.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/src/main/res/values-de/strings.xml

@@ -162,7 +162,7 @@
     <string name="settings_wifi_val">Nur Entwicklermodus — noch nicht implementiert</string>
     <string name="settings_about">Über</string>
     <string name="settings_app_version">App-Version</string>
-    <string name="settings_app_version_val">0.4.0  (Phase 02 — USB-C + DENM TX)</string>
+    <string name="settings_app_version_val">0.5.0  (Phase 03 — ESP32-C5-Seriellverbindung + CAM vom Smartphone)</string>
     <string name="settings_connection">Verbindung</string>
     <string name="settings_usb_auto_detect">OBU per USB-C automatisch erkennen</string>
     <string name="settings_usb_manual_ip">OBU-IP (manuell)</string>
@@ -170,10 +170,6 @@
     <string name="settings_obu_hardware_cit_one">CiT One</string>
     <string name="settings_obu_hardware_esp32">ESP32-C5</string>
     <string name="settings_obu_hardware_esp32_note">Der ESP32-C5 arbeitet als „dummer" Transceiver: CAM wird auf dem Smartphone erstellt und kodiert, über USB-Seriell an den ESP32 gesendet und über ITS-G5 gesendet. Auf diesem Pfad gibt es keinen MQTT-Broker und keine DENM-Use-Case-Engine — siehe den CAM-Pinger im V2X-Monitor für ein manuelles Testwerkzeug.</string>
-    <string name="settings_esp32_rx_mode">CAM-Empfang</string>
-    <string name="settings_esp32_rx_mode_send_only">Nur senden</string>
-    <string name="settings_esp32_rx_mode_send_and_receive">Senden &amp; Empfangen</string>
-    <string name="settings_esp32_rx_mode_desc">„Nur senden" ignoriert von nahen Stationen empfangene CAM (der ESP32 empfängt sie physisch weiterhin — der Empfänger kann nicht abgeschaltet werden, ohne auch das Senden zu unterbrechen — sie werden nur nicht von der App verarbeitet). Nützlich, um den Sendepfad isoliert zu testen.</string>
     <string name="settings_usb_transport">Aktiver Transport</string>
     <string name="settings_transport_usbc">USB-C</string>
     <string name="settings_transport_wifi">WLAN</string>
@@ -270,7 +266,7 @@
     <string name="settings_platform">Plattform</string>
     <string name="settings_platform_val">Android / Kotlin / Jetpack Compose</string>
     <string name="settings_project">Projekt</string>
-    <string name="settings_project_val">MicrOBU — HAW Hamburg</string>
+    <string name="settings_project_val">MicrOBU — HAW Hamburg &amp; consider it GmbH</string>
 
     <!-- Phase A: Trips (bottom nav) -->
     <string name="nav_trips">Fahrten</string>