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/enums.py

@@ -50,6 +50,21 @@ class ItemRarity(Enum):
     LEGENDARY = "legendary"     # Orange/gold - best items
 
 
+class AffixType(Enum):
+    """Types of item affixes for procedural item generation."""
+
+    PREFIX = "prefix"   # Appears before item name: "Flaming Dagger"
+    SUFFIX = "suffix"   # Appears after item name: "Dagger of Strength"
+
+
+class AffixTier(Enum):
+    """Affix power tiers determining bonus magnitudes."""
+
+    MINOR = "minor"           # Weaker bonuses, rolls on RARE items
+    MAJOR = "major"           # Medium bonuses, rolls on EPIC items
+    LEGENDARY = "legendary"   # Strongest bonuses, LEGENDARY only
+
+
 class StatType(Enum):
     """Character attribute types."""