feat(api): integrate equipment stats into combat damage system

Equipment-Combat Integration:
- Update Stats damage formula from STR//2 to int(STR*0.75) for better scaling
- Add spell_power system for magical weapons (staves, wands)
- Add spell_power_bonus field to Stats model with spell_power property
- Add spell_power field to Item model with is_magical_weapon() method
- Update Character.get_effective_stats() to populate spell_power_bonus

Combatant Model Updates:
- Add weapon property fields (crit_chance, crit_multiplier, damage_type)
- Add elemental weapon support (elemental_damage_type, physical_ratio, elemental_ratio)
- Update serialization to handle new weapon properties

DamageCalculator Refactoring:
- Remove weapon_damage parameter from calculate_physical_damage()
- Use attacker_stats.damage directly (includes weapon bonus)
- Use attacker_stats.spell_power for magical damage calculations

Combat Service Updates:
- Extract weapon properties in _create_combatant_from_character()
- Use stats.damage_bonus for enemy combatants from templates
- Remove hardcoded _get_weapon_damage() method
- Handle elemental weapons with split damage in _execute_attack()

Item Generation Updates:
- Add base_spell_power to BaseItemTemplate dataclass
- Add ARCANE damage type to DamageType enum
- Add magical weapon templates (wizard_staff, arcane_staff, wand, crystal_wand)

Test Updates:
- Update test_stats.py for new damage formula (0.75 scaling)
- Update test_character.py for equipment bonus calculations
- Update test_damage_calculator.py for new API signatures
- Update test_combat_service.py mock fixture for equipped attribute

Tests: 174 passing

api/app/models/character.py

@@ -13,7 +13,7 @@ from app.models.stats import Stats
 from app.models.items import Item
 from app.models.skills import PlayerClass, SkillNode
 from app.models.effects import Effect
-from app.models.enums import EffectType, StatType
+from app.models.enums import EffectType, StatType, ItemType
 from app.models.origins import Origin
 
 
@@ -92,7 +92,11 @@ class Character:
 
         This is the CRITICAL METHOD that combines:
         1. Base stats (from character)
-        2. Equipment bonuses (from equipped items)
+        2. Equipment bonuses (from equipped items):
+           - stat_bonuses dict applied to corresponding stats
+           - Weapon damage added to damage_bonus
+           - Weapon spell_power added to spell_power_bonus
+           - Armor defense/resistance added to defense_bonus/resistance_bonus
         3. Skill tree bonuses (from unlocked skills)
         4. Active effect modifiers (buffs/debuffs)
 
@@ -100,18 +104,30 @@ class Character:
             active_effects: Currently active effects on this character (from combat)
 
         Returns:
-            Stats instance with all modifiers applied
+            Stats instance with all modifiers applied (including computed
+            damage, defense, resistance properties that incorporate bonuses)
         """
         # Start with a copy of base stats
         effective = self.base_stats.copy()
 
         # Apply equipment bonuses
         for item in self.equipped.values():
+            # Apply stat bonuses from item (e.g., +3 strength)
             for stat_name, bonus in item.stat_bonuses.items():
                 if hasattr(effective, stat_name):
                     current_value = getattr(effective, stat_name)
                     setattr(effective, stat_name, current_value + bonus)
 
+            # Add weapon damage and spell_power to bonus fields
+            if item.item_type == ItemType.WEAPON:
+                effective.damage_bonus += item.damage
+                effective.spell_power_bonus += item.spell_power
+
+            # Add armor defense and resistance to bonus fields
+            if item.item_type == ItemType.ARMOR:
+                effective.defense_bonus += item.defense
+                effective.resistance_bonus += item.resistance
+
         # Apply skill tree bonuses
         skill_bonuses = self._get_skill_bonuses()
         for stat_name, bonus in skill_bonuses.items():