feat(api): implement Diablo-style item affix system

Add procedural item generation with affix naming system:
- Items with RARE/EPIC/LEGENDARY rarity get dynamic names
- Prefixes (e.g., "Flaming") add elemental damage, material bonuses
- Suffixes (e.g., "of Strength") add stat bonuses
- Affix count scales with rarity: RARE=1, EPIC=2, LEGENDARY=3

New files:
- models/affixes.py: Affix and BaseItemTemplate dataclasses
- services/affix_loader.py: YAML-based affix pool loading
- services/base_item_loader.py: Base item template loading
- services/item_generator.py: Main procedural generation service
- data/affixes/prefixes.yaml: 14 prefix definitions
- data/affixes/suffixes.yaml: 15 suffix definitions
- data/base_items/weapons.yaml: 12 weapon templates
- data/base_items/armor.yaml: 12 armor templates
- tests/test_item_generator.py: 34 comprehensive tests

Modified:
- enums.py: Added AffixType and AffixTier enums
- items.py: Added affix tracking fields (applied_affixes, generated_name)

Example output: "Frozen Dagger of the Bear" (EPIC with ice damage + STR/CON)

api/app/models/items.py

@@ -81,6 +81,24 @@ class Item:
     required_level: int = 1
     required_class: Optional[str] = None
 
+    # Affix tracking (for procedurally generated items)
+    applied_affixes: List[str] = field(default_factory=list)  # List of affix_ids
+    base_template_id: Optional[str] = None  # ID of base item template used
+    generated_name: Optional[str] = None  # Full generated name with affixes
+    is_generated: bool = False  # True if created by item generator
+
+    def get_display_name(self) -> str:
+        """
+        Get the item's display name.
+
+        For generated items, returns the affix-enhanced name.
+        For static items, returns the base name.
+
+        Returns:
+            Display name string
+        """
+        return self.generated_name or self.name
+
     def is_weapon(self) -> bool:
         """Check if this item is a weapon."""
         return self.item_type == ItemType.WEAPON
@@ -166,6 +184,8 @@ class Item:
         if self.elemental_damage_type:
             data["elemental_damage_type"] = self.elemental_damage_type.value
         data["effects_on_use"] = [effect.to_dict() for effect in self.effects_on_use]
+        # Include display_name for convenience
+        data["display_name"] = self.get_display_name()
         return data
 
     @classmethod
@@ -215,6 +235,11 @@ class Item:
             resistance=data.get("resistance", 0),
             required_level=data.get("required_level", 1),
             required_class=data.get("required_class"),
+            # Affix tracking fields
+            applied_affixes=data.get("applied_affixes", []),
+            base_template_id=data.get("base_template_id"),
+            generated_name=data.get("generated_name"),
+            is_generated=data.get("is_generated", False),
         )
 
     def __repr__(self) -> str: