chore(bridge): disable IMU support by default

IMU sensor pipeline is not yet stable; default no_imu to True so it must be explicitly opted into with --no-no-imu or a future --imu flag.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/switch_pico_bridge/controller_uart_bridge.py

@@ -819,7 +819,7 @@ class BridgeConfig:
     swap_abxy_ids: set[str]
     swap_abxy_global: bool
     debug_imu: bool = False
-    no_imu: bool = False
+    no_imu: bool = True
     gyro_scale: float = 1.0