adding abilities, created skill tree template and unlock mechanics

api/app/data/abilities/epidemic.yaml

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+# Epidemic - Necromancer Dark Affliction ultimate
+# Ultimate multi-DoT all enemies
+
+ability_id: "epidemic"
+name: "Epidemic"
+description: "Unleash a devastating epidemic that afflicts all enemies with multiple diseases"
+ability_type: "spell"
+base_power: 60
+damage_type: "shadow"
+scaling_stat: "intelligence"
+scaling_factor: 0.7
+mana_cost: 60
+cooldown: 6
+is_aoe: true
+target_count: 0
+effects_applied:
+  - effect_id: "epidemic_plague"
+    name: "Epidemic"
+    effect_type: "dot"
+    duration: 5
+    power: 20
+    stat_affected: null
+    stacks: 1
+    max_stacks: 1
+    source: "epidemic"
+  - effect_id: "weakened"
+    name: "Weakened"
+    effect_type: "debuff"
+    duration: 5
+    power: 25
+    stat_affected: null
+    stacks: 1
+    max_stacks: 1
+    source: "epidemic"