adding abilities, created skill tree template and unlock mechanics

api/app/data/abilities/shadowstep.yaml

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+# Shadowstep - Assassin Shadow Dancer ability
+# Teleport and backstab
+
+ability_id: "shadowstep"
+name: "Shadowstep"
+description: "Vanish into the shadows and reappear behind your target, striking from behind"
+ability_type: "skill"
+base_power: 18
+damage_type: "physical"
+scaling_stat: "dexterity"
+scaling_factor: 0.6
+mana_cost: 10
+cooldown: 2
+is_aoe: false
+target_count: 1
+effects_applied: []