[2pts] Create Enemy abstract class and concrete enemy types

[github-actions]

Description

Create abstract Enemy class and concrete enemy type implementations.

Depends on: Character base class issue

Enemy Abstract Class

Inherits from Character and adds:

• ExperienceReward (int)
• GoldReward (int)
• LootTable (List)
• abstract GetAttackDescription() method

Concrete Enemy Types

Goblin

• Low stats (low health, attack, defense)
• Distinct flavor text in GetAttackDescription()

Orc

• High health
• Medium attack and defense
• Distinct flavor text in GetAttackDescription()

Dragon

• Boss tier stats (very high in all categories)
• Distinct flavor text in GetAttackDescription()

Acceptance Criteria

• Enemy abstract class inherits from Character
• ExperienceReward property added
• GoldReward property added
• LootTable property (List) added
• Abstract GetAttackDescription() method declared
• Goblin concrete class implemented with low stats
• Orc concrete class implemented with high health
• Dragon concrete class implemented with boss-tier stats
• Each enemy type has distinct flavor text
• All classes documented with XML comments