PNG Stalkers v41 Sound + Ground Fix

Changes from v40:
- Rebuilt sounds.json from scratch.
- Re-added chase_1.ogg trimmed to first 4 seconds.
- Added fallback sound event stalker_chase.
- Added hurt fallback event too.
- test command now plays vanilla bell first, then custom sounds:
  /function pngstalksafe:test_chase_sound
- Chase sound now also works in Creative for testing.
- Visual PNG offsets lowered so the stalkers' feet are near the ground.
- Movement is yaw-only now: the hidden mob faces the target, pitch is clamped to 0, then it moves forward.
- Added gentle downward correction to stop airborne drifting while chasing.

IMPORTANT:
After replacing the jar, fully quit Minecraft and reopen it. /reload alone may not reload new sounds.
