Monster Pack

## v1.0.1 — Bug Fixes & Polish

### 🐛 Bug Fixes
- Fixed spawner packs spawning only 1 mob instead of 4-6 (pack extras were being queued instead of spawned)
- Fixed mob spawn failures in indoor/enclosed spaces (added 3-tier fallback spawn system)
- Fixed memory leak when server restarts (PENDING_BY_DIM was never cleared)
- Fixed potential NPE when spawner BlockEntity was missing
- Fixed crash on inverted pack_size_min > pack_size_max config

### ✨ Improvements  
- Default spawner cooldown reduced: 5 min → 1 min (more active gameplay)
- Pack members now spawn with proper 2-block headroom (no suffocation)
- Tier 3 fallback adds slight position offset to prevent mob stacking
- Multiplayer-optimized: spawners scanned once per tick regardless of player count
- Logging cleaned up (per-spawn details moved to DEBUG level)
- Improved error messages for spawn failures

### 📚 Documentation
- Added comprehensive Javadoc for filter mode behavior
- Thread-safety expectations documented for internal state