feat: add standard actuator command interface

[jimsynz]

Summary

Introduces a standardised interface for sending commands to actuators, supporting both pubsub delivery (for orchestration, logging, replay) and direct GenServer delivery (for time-critical control).

Command Message Types

Command	Description
Position	Target position with optional velocity/duration hints
Velocity	Target velocity with optional duration
Effort	Target torque/force with optional duration
Trajectory	Waypoints with position/velocity/acceleration/time
Stop	Cease motion (:immediate or :decelerate)
Hold	Actively maintain current position

Delivery Module (BB.Actuator)

Three delivery methods for each command type:

• Pubsub (set_position/4, etc.) - For orchestration, enables logging and replay
• Direct cast (set_position!/4, etc.) - Fire-and-forget, lower latency
• Synchronous (set_position_sync/5, etc.) - Returns acknowledgement or error

Enhanced Motion Messages

• BeginMotion - Added command_id and command_type for correlation
• EndMotion - Added command_id for correlation

Example Usage

# Pubsub delivery (kinematics/orchestration)
BB.Actuator.set_position(MyRobot, [:base_link, :shoulder, :servo], 1.57)

# Direct delivery (time-critical control)
BB.Actuator.set_position!(MyRobot, :shoulder_servo, 1.57)

# Synchronous with acknowledgement
{:ok, :accepted} = BB.Actuator.set_position_sync(MyRobot, :shoulder_servo, 1.57)

# Trajectory
waypoints = [
  [position: 0.0, velocity: 0.0, acceleration: 0.5, time_from_start: 0],
  [position: 0.5, velocity: 0.3, acceleration: 0.0, time_from_start: 200],
  [position: 1.0, velocity: 0.0, acceleration: -0.5, time_from_start: 400]
]
BB.Actuator.follow_trajectory(MyRobot, [:shoulder, :servo], waypoints)

Test plan

• All command message types compile and validate correctly
• BB.Actuator delivery module compiles
• Enhanced BeginMotion/EndMotion backward compatible
• All 457 tests pass
• mix check --no-retry passes