Balance Issue: Fisherman Tower Is Overpowered

## Description
The fisherman tower can be spammed to trivialize the game. While the mechanic combination (damage vs net) is interesting, the current balance makes fishermen significantly stronger than other options.

## Expected Improvement
- Rebalance fisherman tower effectiveness
- Adjust cost, cooldown, range, or effectiveness of the net mechanic
- Encourage mixed tower usage rather than single-tower spamming

## Notes
- The mechanic itself is good and worth keeping
- Balance pass needed rather than a redesign