adding abilities, created skill tree template and unlock mechanics

api/app/data/abilities/shield_wall.yaml

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+# Shield Wall - Vanguard Shield Bearer ability
+# Defensive buff reducing damage
+
+ability_id: "shield_wall"
+name: "Shield Wall"
+description: "Raise your shield to block incoming attacks, reducing damage by 50% for 3 turns"
+ability_type: "defend"
+base_power: 0
+damage_type: null
+scaling_stat: "constitution"
+scaling_factor: 0.3
+mana_cost: 12
+cooldown: 4
+is_aoe: false
+target_count: 1
+effects_applied:
+  - effect_id: "shield_wall_buff"
+    name: "Shield Wall"
+    effect_type: "buff"
+    duration: 3
+    power: 50
+    stat_affected: null
+    stacks: 1
+    max_stacks: 1
+    source: "shield_wall"