Implement Modular Tower Synergy System

[mihaid11]

Create a flexible system for tower synergies (buffs/combined effects) that:

• Detects proximity between towers (2-4 towers required)
• Allows dynamic effect registration
• Does not implement specific synergies yet (will be added via future issues)

Requirements:

• Synergy Triggers
• Range-based detection
• Configurable tower combinations (2-4 towers)
• Effect Types (Framework Only)
• Damage multipliers
• New attack patterns

Priority: Medium