feat: Add MTGJSON data loading and download scripts

- Fix MtgSet model to match database schema (removed created_at, added image column)
- Create load_mtgjson_data.py script to load AllSetFiles, AllPrintings.psql, and other MTGJSON data
- Create download_mtgjson_data.py script to download MTGJSON API data files
- Add SPEC_synergy-mapping-engine.md documentation

API endpoints are now working (200 OK) but database needs data loading via download_mtgjson_data.py
then load_mtgjson_data.py

backend/app/models/mtg_models.py

@@ -26,7 +26,7 @@ class MtgSet(Base):
     icon_svg_url = Column(Text, nullable=True)
     parent_code = Column(String(10), nullable=True)
     mtgo_code = Column(String(10), nullable=True)
-    created_at = Column(DateTime, server_default=func.now())
+    image = Column(Text, nullable=True)  # Card image URL from MTGJSON
     updated_at = Column(DateTime, server_default=func.now(), onupdate=func.now())
 
     # Relationships
@@ -55,7 +55,7 @@ class MtgCard(Base):
     numbers = Column(String(100), nullable=True)
     identifiers = Column(Text, nullable=True)  # JSON string
     images = Column(Text, nullable=True)  # JSON string
-    created_at = Column(DateTime, server_default=func.now())
+    image = Column(Text, nullable=True)  # Card image URL from MTGJSON
     updated_at = Column(DateTime, server_default=func.now(), onupdate=func.now())
 
     # Relationships