Fix missing features and improve code quality

Features fixed:
- Added chat filter functionality (block/warn/censor modes)
- Fixed spy command to monitor all chat messages
- Added proper spy notifications for global/local chat

Code quality improvements:
- Created PlayerUtil to eliminate code duplication in player lookup
- Refactored ChatListener into smaller, focused methods
- Added Constants class to replace magic numbers
- Improved SOLID principles compliance
- Fixed all compilation warnings

All features from README are now implemented and working.

src/main/java/com/loki/lochat/config/ConfigManager.java

@@ -154,7 +154,7 @@ public class ConfigManager {
     }
 
     public int getLocalRadius() {
-        return config.getInt("chat.local.radius", 100);
+        return config.getInt("chat.local.radius", com.loki.lochat.utils.Constants.DEFAULT_LOCAL_RADIUS);
     }
 
     public String getLocalPrefix() {