Ensure ros controller doesn't timeout on cmd_vel

The ros controller will timeout if it doesn't receive a cmd_vel message
in a given period, stopping the wheels.
webui sends messages at 100ms intervals, so the update rate needs to be 10Hz
This may need to be reviewed when using other input systems.

ansible/setup_robot.yml

@@ -45,5 +45,20 @@
     #     state: present
     #     update_cache: true
 
+    # I2C Fast Mode (400 kHz) reduces SSD1306 OLED frame transfers from ~95 ms
+    # to ~24 ms, shrinking the window in which the kernel I2C adapter lock blocks
+    # motor writes on the shared /dev/i2c-1 bus.
+    - name: Set I2C bus speed to 400 kHz
+      lineinfile:
+        path: /boot/firmware/config.txt
+        regexp: '^dtparam=i2c_arm_baudrate='
+        line: 'dtparam=i2c_arm_baudrate=400000'
+      notify: Reboot required
+
+  handlers:
+    - name: Reboot required
+      debug:
+        msg: "config.txt updated — reboot the Pi to apply I2C speed change"
+
   roles:
     - geerlingguy.docker