adding abilities, created skill tree template and unlock mechanics

api/app/data/abilities/death_mark.yaml

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+# Death Mark - Assassin Shadow Dancer ability
+# Mark target for bonus damage
+
+ability_id: "death_mark"
+name: "Death Mark"
+description: "Mark your target for death. Your next attack deals 200% damage"
+ability_type: "skill"
+base_power: 0
+damage_type: null
+scaling_stat: "dexterity"
+scaling_factor: 0.0
+mana_cost: 30
+cooldown: 4
+is_aoe: false
+target_count: 1
+effects_applied:
+  - effect_id: "marked_for_death"
+    name: "Marked for Death"
+    effect_type: "debuff"
+    duration: 2
+    power: 100
+    stat_affected: null
+    stacks: 1
+    max_stacks: 1
+    source: "death_mark"