adding abilities, created skill tree template and unlock mechanics

api/app/data/abilities/cleave.yaml

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+# Cleave - Vanguard Weapon Master ability
+# AoE attack hitting all enemies
+
+ability_id: "cleave"
+name: "Cleave"
+description: "Swing your weapon in a wide arc, hitting all enemies"
+ability_type: "attack"
+base_power: 20
+damage_type: "physical"
+scaling_stat: "strength"
+scaling_factor: 0.5
+mana_cost: 15
+cooldown: 2
+is_aoe: true
+target_count: 0
+effects_applied: []