fix: Yaris 2013 OBD compatibility hardening

- _decode_odometer: catch all exceptions and return None instead of raising.
  PID 0xA6 (odometer) is not guaranteed on 2013 Toyota Yaris — a garbage
  response or unsupported PID previously raised ValueError through python-obd's
  decoder, which app_obd._query() caught and treated as a lost connection,
  killing the entire OBD session. Now it gracefully returns None.

- connect_obd: reset all sensor globals (rpm, coolant_temp, fuel_level,
  throttle_position, mil_on, dtc_codes, odometer, timestamps) on each new
  connection so the UI doesn't display stale readings from the previous
  ignition cycle while fresh polls are completing.

- yaris-obd.service: add commented OBD_PROTOCOL=6 hint for post-confirmation
  pinning (eliminates 3-5s auto-probe delay after first confirmed connection).

Co-authored-by: Copilot <[email protected]>

deploy/yaris-obd.service

@@ -12,6 +12,11 @@ WorkingDirectory=/home/yaris/app/yaris-obd
 # the log file promptly instead of sitting in Python's stdout buffer indefinitely
 # when it's redirected to a file instead of a TTY.
 Environment=PYTHONUNBUFFERED=1
+# Once OBD is confirmed working on this car, pin the protocol to skip the
+# 3-5s auto-detect probe on every ignition-on: e.g. OBD_PROTOCOL=6 for
+# ISO 15765-4 CAN 11-bit 500kbps (correct for 2013 Toyota Yaris).
+# Leave unset during initial setup so auto-detect can find the right value.
+#Environment=OBD_PROTOCOL=6
 ExecStart=/home/yaris/app/yaris-obd/venv/bin/python app.py
 Restart=on-failure
 RestartSec=5