Add continuous world-worker follow behaviour

[SimGamerJen]

Summary

Builds directly on the validated target-navigation checkpoint and adds session-only continuous following of the local player.

Commands

• hpWorld follow [slot] [standOffMetres]
• hpWorld unfollow [slot]

Aliases:

• followme, trail
• followstop, stopfollow

Behaviour

• reuses the validated target-navigation + bounded-yaw locomotion pipeline
• continuously retargets the active navigation target to the player's live position every frame
• preserves the existing native-style gait, steering, acceleration/braking, terrain following and persistence
• default stand-off: 1.8 m (clamped 0.75–5.0 m)
• hysteresis prevents constant foot-shuffling: after stopping, the worker resumes only once the player is roughly 0.75 m beyond the stand-off
• stops immediately if the player moves inside the requested stand-off while the worker is approaching
• pauses if player/worker data becomes unavailable
• direct-follow range remains capped at 100 m for this prototype
• unfollow cleanly stops any active follow motion and persists the worker's final position

Persistence

The resulting worker position persists normally, but FOLLOW mode itself is deliberately session-only for this prototype. Reloading a save will not make a worker automatically resume chasing the player.

Test focus

1. Confirm [WorldFollow] Loaded ... continuous-follow-1 appears.
2. Place A outdoors and run hpWorld follow A.
3. Walk away slowly and confirm A starts, continually steers toward the moving player, and stops around the stand-off.
4. Hover around the stand-off and confirm A does not constantly take tiny corrective steps.
5. Open the gap again and confirm A resumes automatically.
6. Walk across A's path / change direction sharply and confirm live retargeting remains smooth and jitter-free.
7. Try hpWorld follow A 2.5 to update the stand-off while already following.
8. Run hpWorld unfollow A while moving and while waiting; both should cancel cleanly.

No obstacle avoidance or pathfinding is introduced in this PR.

[SimGamerJen]

Test result — FULL PASS

The remaining continuous-follow cases are now validated in-game.

• Live stand-off update while already following: PASS. hpWorld follow A 2.5 updates standOff=2.50 and resumeAt=3.25, then the worker resumes once the gap reaches ~3.26–3.28 m and subsequently settles cleanly at ~2.50 m.
• unfollow while actively moving: PASS. Active curved locomotion stops immediately with reason=follow-cancelled, followed by FOLLOW STOP A reason=requested and a successful command result.
• Continuous retargeting remains smooth through large heading changes during the 2.5 m follow test.

Combined with the earlier visual and log validation, PR #24 is now the known-good continuous-follow checkpoint.