adding abilities, created skill tree template and unlock mechanics

api/app/data/abilities/drain_life.yaml

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+# Drain Life - Necromancer Dark Affliction ability
+# Shadow damage + self-heal
+
+ability_id: "drain_life"
+name: "Drain Life"
+description: "Drain the life force from your enemy, dealing shadow damage and healing yourself"
+ability_type: "spell"
+base_power: 18
+damage_type: "shadow"
+scaling_stat: "intelligence"
+scaling_factor: 0.5
+mana_cost: 12
+cooldown: 1
+is_aoe: false
+target_count: 1
+effects_applied:
+  - effect_id: "life_drain"
+    name: "Life Drained"
+    effect_type: "hot"
+    duration: 1
+    power: 9
+    stat_affected: null
+    stacks: 1
+    max_stacks: 1
+    source: "drain_life"