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/base_items/weapons.yaml

@@ -0,0 +1,182 @@
+# Base Weapon Templates for Procedural Generation
+#
+# These templates define the foundation that affixes attach to.
+# Example: "Dagger" + "Flaming" prefix = "Flaming Dagger"
+#
+# Template Structure:
+#   template_id: Unique identifier
+#   name: Base item name
+#   item_type: "weapon"
+#   description: Flavor text
+#   base_damage: Weapon damage
+#   base_value: Gold value
+#   damage_type: "physical" (default)
+#   crit_chance: Critical hit chance (0.0-1.0)
+#   crit_multiplier: Crit damage multiplier
+#   required_level: Min level to use/drop
+#   drop_weight: Higher = more common (1.0 = standard)
+#   min_rarity: Minimum rarity for this template
+
+weapons:
+  # ==================== ONE-HANDED SWORDS ====================
+  dagger:
+    template_id: "dagger"
+    name: "Dagger"
+    item_type: "weapon"
+    description: "A small, quick blade for close combat"
+    base_damage: 6
+    base_value: 15
+    damage_type: "physical"
+    crit_chance: 0.08
+    crit_multiplier: 2.0
+    required_level: 1
+    drop_weight: 1.5
+
+  short_sword:
+    template_id: "short_sword"
+    name: "Short Sword"
+    item_type: "weapon"
+    description: "A versatile one-handed blade"
+    base_damage: 10
+    base_value: 30
+    damage_type: "physical"
+    crit_chance: 0.06
+    crit_multiplier: 2.0
+    required_level: 1
+    drop_weight: 1.3
+
+  longsword:
+    template_id: "longsword"
+    name: "Longsword"
+    item_type: "weapon"
+    description: "A standard warrior's blade"
+    base_damage: 14
+    base_value: 50
+    damage_type: "physical"
+    crit_chance: 0.05
+    crit_multiplier: 2.0
+    required_level: 3
+    drop_weight: 1.0
+
+  # ==================== TWO-HANDED WEAPONS ====================
+  greatsword:
+    template_id: "greatsword"
+    name: "Greatsword"
+    item_type: "weapon"
+    description: "A massive two-handed blade"
+    base_damage: 22
+    base_value: 100
+    damage_type: "physical"
+    crit_chance: 0.04
+    crit_multiplier: 2.5
+    required_level: 5
+    drop_weight: 0.7
+    min_rarity: "uncommon"
+
+  # ==================== AXES ====================
+  hatchet:
+    template_id: "hatchet"
+    name: "Hatchet"
+    item_type: "weapon"
+    description: "A small throwing axe"
+    base_damage: 8
+    base_value: 20
+    damage_type: "physical"
+    crit_chance: 0.06
+    crit_multiplier: 2.2
+    required_level: 1
+    drop_weight: 1.2
+
+  battle_axe:
+    template_id: "battle_axe"
+    name: "Battle Axe"
+    item_type: "weapon"
+    description: "A heavy axe designed for combat"
+    base_damage: 16
+    base_value: 60
+    damage_type: "physical"
+    crit_chance: 0.05
+    crit_multiplier: 2.3
+    required_level: 4
+    drop_weight: 0.9
+
+  # ==================== BLUNT WEAPONS ====================
+  club:
+    template_id: "club"
+    name: "Club"
+    item_type: "weapon"
+    description: "A simple wooden club"
+    base_damage: 7
+    base_value: 10
+    damage_type: "physical"
+    crit_chance: 0.04
+    crit_multiplier: 2.0
+    required_level: 1
+    drop_weight: 1.5
+
+  mace:
+    template_id: "mace"
+    name: "Mace"
+    item_type: "weapon"
+    description: "A flanged mace for crushing armor"
+    base_damage: 12
+    base_value: 40
+    damage_type: "physical"
+    crit_chance: 0.05
+    crit_multiplier: 2.0
+    required_level: 2
+    drop_weight: 1.0
+
+  # ==================== STAVES ====================
+  quarterstaff:
+    template_id: "quarterstaff"
+    name: "Quarterstaff"
+    item_type: "weapon"
+    description: "A simple wooden staff"
+    base_damage: 6
+    base_value: 10
+    damage_type: "physical"
+    crit_chance: 0.05
+    crit_multiplier: 2.0
+    required_level: 1
+    drop_weight: 1.2
+
+  wizard_staff:
+    template_id: "wizard_staff"
+    name: "Wizard Staff"
+    item_type: "weapon"
+    description: "A staff attuned to magical energy"
+    base_damage: 8
+    base_value: 45
+    damage_type: "physical"
+    crit_chance: 0.05
+    crit_multiplier: 2.0
+    required_level: 3
+    drop_weight: 0.8
+
+  # ==================== RANGED ====================
+  shortbow:
+    template_id: "shortbow"
+    name: "Shortbow"
+    item_type: "weapon"
+    description: "A compact bow for quick shots"
+    base_damage: 8
+    base_value: 25
+    damage_type: "physical"
+    crit_chance: 0.07
+    crit_multiplier: 2.0
+    required_level: 1
+    drop_weight: 1.1
+
+  longbow:
+    template_id: "longbow"
+    name: "Longbow"
+    item_type: "weapon"
+    description: "A powerful bow with excellent range"
+    base_damage: 14
+    base_value: 55
+    damage_type: "physical"
+    crit_chance: 0.08
+    crit_multiplier: 2.2
+    required_level: 4
+    drop_weight: 0.9