adding abilities, created skill tree template and unlock mechanics

api/app/data/abilities/rain_of_arrows.yaml

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+# Rain of Arrows - Wildstrider Marksmanship ultimate
+# Ultimate AoE attack
+
+ability_id: "rain_of_arrows"
+name: "Rain of Arrows"
+description: "Call down a devastating rain of arrows upon all enemies"
+ability_type: "attack"
+base_power: 85
+damage_type: "physical"
+scaling_stat: "dexterity"
+scaling_factor: 0.7
+mana_cost: 55
+cooldown: 5
+is_aoe: true
+target_count: 0
+effects_applied:
+  - effect_id: "pinned"
+    name: "Pinned"
+    effect_type: "debuff"
+    duration: 1
+    power: 50
+    stat_affected: null
+    stacks: 1
+    max_stacks: 1
+    source: "rain_of_arrows"