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/stats.py

@@ -22,12 +22,18 @@ class Stats:
         wisdom: Perception and insight, affects magical resistance
         charisma: Social influence, affects NPC interactions
         luck: Fortune and fate, affects critical hits, loot, and random outcomes
+        damage_bonus: Flat damage bonus from equipped weapons (default 0)
+        spell_power_bonus: Flat spell power bonus from staves/wands (default 0)
+        defense_bonus: Flat defense bonus from equipped armor (default 0)
+        resistance_bonus: Flat resistance bonus from equipped armor (default 0)
 
     Computed Properties:
         hit_points: Maximum HP = 10 + (constitution × 2)
         mana_points: Maximum MP = 10 + (intelligence × 2)
-        defense: Physical defense = constitution // 2
-        resistance: Magical resistance = wisdom // 2
+        damage: Physical damage = int(strength × 0.75) + damage_bonus
+        spell_power: Spell power = int(intelligence × 0.75) + spell_power_bonus
+        defense: Physical defense = (constitution // 2) + defense_bonus
+        resistance: Magical resistance = (wisdom // 2) + resistance_bonus
     """
 
     strength: int = 10
@@ -38,6 +44,12 @@ class Stats:
     charisma: int = 10
     luck: int = 8
 
+    # Equipment bonus fields (populated by get_effective_stats())
+    damage_bonus: int = 0         # From weapons (physical damage)
+    spell_power_bonus: int = 0    # From staves/wands (magical damage)
+    defense_bonus: int = 0        # From armor
+    resistance_bonus: int = 0     # From armor
+
     @property
     def hit_points(self) -> int:
         """
@@ -62,29 +74,65 @@ class Stats:
         """
         return 10 + (self.intelligence * 2)
 
+    @property
+    def damage(self) -> int:
+        """
+        Calculate total physical damage from strength and equipment.
+
+        Formula: int(strength * 0.75) + damage_bonus
+
+        The damage_bonus comes from equipped weapons and is populated
+        by Character.get_effective_stats().
+
+        Returns:
+            Total physical damage value
+        """
+        return int(self.strength * 0.75) + self.damage_bonus
+
+    @property
+    def spell_power(self) -> int:
+        """
+        Calculate spell power from intelligence and equipment.
+
+        Formula: int(intelligence * 0.75) + spell_power_bonus
+
+        The spell_power_bonus comes from equipped staves/wands and is
+        populated by Character.get_effective_stats().
+
+        Returns:
+            Total spell power value
+        """
+        return int(self.intelligence * 0.75) + self.spell_power_bonus
+
     @property
     def defense(self) -> int:
         """
-        Calculate physical defense from constitution.
+        Calculate physical defense from constitution and equipment.
 
-        Formula: constitution // 2
+        Formula: (constitution // 2) + defense_bonus
+
+        The defense_bonus comes from equipped armor and is populated
+        by Character.get_effective_stats().
 
         Returns:
             Physical defense value (damage reduction)
         """
-        return self.constitution // 2
+        return (self.constitution // 2) + self.defense_bonus
 
     @property
     def resistance(self) -> int:
         """
-        Calculate magical resistance from wisdom.
+        Calculate magical resistance from wisdom and equipment.
 
-        Formula: wisdom // 2
+        Formula: (wisdom // 2) + resistance_bonus
+
+        The resistance_bonus comes from equipped armor and is populated
+        by Character.get_effective_stats().
 
         Returns:
             Magical resistance value (spell damage reduction)
         """
-        return self.wisdom // 2
+        return (self.wisdom // 2) + self.resistance_bonus
 
     @property
     def crit_bonus(self) -> float:
@@ -171,6 +219,10 @@ class Stats:
             wisdom=data.get("wisdom", 10),
             charisma=data.get("charisma", 10),
             luck=data.get("luck", 8),
+            damage_bonus=data.get("damage_bonus", 0),
+            spell_power_bonus=data.get("spell_power_bonus", 0),
+            defense_bonus=data.get("defense_bonus", 0),
+            resistance_bonus=data.get("resistance_bonus", 0),
         )
 
     def copy(self) -> 'Stats':
@@ -188,6 +240,10 @@ class Stats:
             wisdom=self.wisdom,
             charisma=self.charisma,
             luck=self.luck,
+            damage_bonus=self.damage_bonus,
+            spell_power_bonus=self.spell_power_bonus,
+            defense_bonus=self.defense_bonus,
+            resistance_bonus=self.resistance_bonus,
         )
 
     def __repr__(self) -> str:
@@ -197,6 +253,7 @@ class Stats:
             f"CON={self.constitution}, INT={self.intelligence}, "
             f"WIS={self.wisdom}, CHA={self.charisma}, LUK={self.luck}, "
             f"HP={self.hit_points}, MP={self.mana_points}, "
+            f"DMG={self.damage}, SP={self.spell_power}, "
             f"DEF={self.defense}, RES={self.resistance}, "
             f"CRIT_BONUS={self.crit_bonus:.1%}, HIT_BONUS={self.hit_bonus:.1%})"
         )