feat: compute base item values by reversing active spell buffs

Extract spell effect mappings from Dictionaries.cs into spell_effects.json.
During item ingestion, compute_base_values() reverses active enchantment
effects to get true base stats:
- base_armor_level: armor without Impenetrability buffs
- base_max_damage: damage without Blood Drinker buffs
- base_attack_bonus: attack without Heart Seeker buffs
- base_melee_defense_bonus: defense without Defender buffs
- base_elemental_damage_vs_monsters: elemental without Spirit Drinker
- base_mana_conversion_bonus: mana conv without Hermetic Link

New columns in ItemCombatStats, exposed in search CTEs.
Frontend: Base Armor and Base Dmg columns (hidden by default, toggle on).
Requires ALTER TABLE migration before deploy.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

inventory-service/database.py

@@ -125,6 +125,14 @@ class ItemCombatStats(Base):
     gear_pk_damage_rating = Column(Integer)
     gear_pk_damage_resist_rating = Column(Integer)
 
+    # Base values (with active spell buffs reversed)
+    base_armor_level = Column(Integer)
+    base_max_damage = Column(Integer)
+    base_attack_bonus = Column(Float)
+    base_melee_defense_bonus = Column(Float)
+    base_elemental_damage_vs_monsters = Column(Float)
+    base_mana_conversion_bonus = Column(Float)
+
 class ItemRequirements(Base):
     """Wield requirements and skill prerequisites."""
     __tablename__ = 'item_requirements'