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/data/affixes/suffixes.yaml

@@ -0,0 +1,155 @@
+# Item Suffix Affixes
+# Suffixes appear after the item name: "Dagger of Strength"
+#
+# Suffix naming convention:
+#   - Minor tier: "of [Stat]" (e.g., "of Strength")
+#   - Major tier: "of the [Animal/Element]" (e.g., "of the Bear")
+#   - Legendary tier: "of the [Mythical]" (e.g., "of the Titan")
+
+suffixes:
+  # ==================== STAT SUFFIXES (MINOR) ====================
+  of_strength:
+    affix_id: "of_strength"
+    name: "of Strength"
+    affix_type: "suffix"
+    tier: "minor"
+    description: "Grants physical power"
+    stat_bonuses:
+      strength: 2
+
+  of_dexterity:
+    affix_id: "of_dexterity"
+    name: "of Dexterity"
+    affix_type: "suffix"
+    tier: "minor"
+    description: "Grants agility and precision"
+    stat_bonuses:
+      dexterity: 2
+
+  of_constitution:
+    affix_id: "of_constitution"
+    name: "of Fortitude"
+    affix_type: "suffix"
+    tier: "minor"
+    description: "Grants endurance"
+    stat_bonuses:
+      constitution: 2
+
+  of_intelligence:
+    affix_id: "of_intelligence"
+    name: "of Intelligence"
+    affix_type: "suffix"
+    tier: "minor"
+    description: "Grants magical aptitude"
+    stat_bonuses:
+      intelligence: 2
+
+  of_wisdom:
+    affix_id: "of_wisdom"
+    name: "of Wisdom"
+    affix_type: "suffix"
+    tier: "minor"
+    description: "Grants insight and perception"
+    stat_bonuses:
+      wisdom: 2
+
+  of_charisma:
+    affix_id: "of_charisma"
+    name: "of Charm"
+    affix_type: "suffix"
+    tier: "minor"
+    description: "Grants social influence"
+    stat_bonuses:
+      charisma: 2
+
+  of_luck:
+    affix_id: "of_luck"
+    name: "of Fortune"
+    affix_type: "suffix"
+    tier: "minor"
+    description: "Grants favor from fate"
+    stat_bonuses:
+      luck: 2
+
+  # ==================== ENHANCED STAT SUFFIXES (MAJOR) ====================
+  of_the_bear:
+    affix_id: "of_the_bear"
+    name: "of the Bear"
+    affix_type: "suffix"
+    tier: "major"
+    description: "Grants the might and endurance of a bear"
+    stat_bonuses:
+      strength: 4
+      constitution: 2
+
+  of_the_fox:
+    affix_id: "of_the_fox"
+    name: "of the Fox"
+    affix_type: "suffix"
+    tier: "major"
+    description: "Grants the cunning and agility of a fox"
+    stat_bonuses:
+      dexterity: 4
+      luck: 2
+
+  of_the_owl:
+    affix_id: "of_the_owl"
+    name: "of the Owl"
+    affix_type: "suffix"
+    tier: "major"
+    description: "Grants the wisdom and insight of an owl"
+    stat_bonuses:
+      intelligence: 3
+      wisdom: 3
+
+  # ==================== DEFENSIVE SUFFIXES ====================
+  of_protection:
+    affix_id: "of_protection"
+    name: "of Protection"
+    affix_type: "suffix"
+    tier: "minor"
+    description: "Offers physical protection"
+    defense_bonus: 3
+
+  of_warding:
+    affix_id: "of_warding"
+    name: "of Warding"
+    affix_type: "suffix"
+    tier: "major"
+    description: "Wards against physical and magical harm"
+    defense_bonus: 5
+    resistance_bonus: 3
+
+  # ==================== LEGENDARY SUFFIXES ====================
+  of_the_titan:
+    affix_id: "of_the_titan"
+    name: "of the Titan"
+    affix_type: "suffix"
+    tier: "legendary"
+    description: "Grants titanic strength and endurance"
+    stat_bonuses:
+      strength: 8
+      constitution: 4
+    required_rarity: "legendary"
+
+  of_the_wind:
+    affix_id: "of_the_wind"
+    name: "of the Wind"
+    affix_type: "suffix"
+    tier: "legendary"
+    description: "Swift as the wind itself"
+    stat_bonuses:
+      dexterity: 8
+      luck: 4
+    crit_chance_bonus: 0.05
+    required_rarity: "legendary"
+
+  of_invincibility:
+    affix_id: "of_invincibility"
+    name: "of Invincibility"
+    affix_type: "suffix"
+    tier: "legendary"
+    description: "Grants supreme protection"
+    defense_bonus: 10
+    resistance_bonus: 8
+    required_rarity: "legendary"