Add selective motor control API

[mvrius]

Add selective motor control API

Motivation

When running Reachy Mini in "always-on" mode (e.g., as an ambient assistant), I want to keep all motors disabled to save power and reduce wear. However, when detecting certain keyword sounds (like a wake word), I want to activate only the antennas to provide visual feedback without moving the head or body.

Changes

• Added optional motors parameter to POST /api/motors/set_mode/{mode} endpoint
• When motors list is provided, only those specific motors are affected
• When motors is omitted or empty, all motors are affected (existing behavior preserved)

Usage

# Disable all motors
curl -X POST http://reachy-mini:8000/api/motors/set_mode/disabled

# Enable only antennas
curl -X POST http://reachy-mini:8000/api/motors/set_mode/enabled \
  -H "Content-Type: application/json" \
  -d '{"motors": ["left_antenna", "right_antenna"]}'

Testing

Tested on Reachy Mini Wireless running version 1.2.4 patched with this PR. Verified that:

• Antennas can be selectively enabled while head/body motors remain disabled
• Position commands work correctly for enabled motors only
• Body stays compliant (no torque) when only antennas are enabled
• Full sequence tested: sleep → disable all → enable antennas only → move antennas (head/body stayed limp) → enable all → wake up