imu: the WT61 on any USB-UART adapter, in the car's frame, on yukart/imu/*

Finds the module itself (every non-modem adapter, 115200 then 9600), so the
adapter can be swapped. Mounting by --forward/--right; attitude from a
complementary filter on gravity (gyro through motion, accelerometer near 1 g);
gravity removed from acceleration; yaw rate left-positive. Never writes to
the module. dialout via SupplementaryGroups.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

deploy/yukart-imu.service

@@ -0,0 +1,19 @@
+[Unit]
+Description=Yukart imu: the WT61 on a USB-UART adapter, as the car's motion on the bus
+Documentation=gitea:yukart/svc-core
+# Tier 2. Ordered after the broker and nothing else: it finds the adapter by itself,
+# whenever it appears.
+After=mosquitto.service
+StartLimitIntervalSec=0
+
+[Service]
+User=mikkeli
+# USB serial adapters belong to dialout: the one right it needs, no sudo.
+SupplementaryGroups=dialout
+# Mounting: add --forward AXIS --right AXIS once the module has its place in the car.
+ExecStart=/usr/local/bin/yukart-imu
+Restart=always
+RestartSec=2
+
+[Install]
+WantedBy=multi-user.target