feat: Add MTGJSON data integration

- Added MTGJSON data downloader (downloads all MTGJSON API v5 files)
- Added MTGJSON data loader (imports data into PostgreSQL)
- Added MTGJSON data uploader (alternative upsert logic)
- Fixed route ordering in card_router.py (/sets before /{card_name})
- Added load_mtgjson_data.py entry point script

MTGJSON data sources:
- AllPrintings.psql.gz (main cards database)
- AllSetFiles.zip (set and card data)
- AllDeckFiles.zip (deck data)
- AllIdentifiers.json.gz (card identifiers)
- CardTypes.json.gz (card types)
- DeckList.json.gz (deck list metadata)
- Keywords.json.gz (card keywords)
- SetList.json.gz (set list metadata)

Note: MTGJSON set.json does NOT contain image URLs. Only cards have image_uris.
Sets have iconSvgUrl (SVG icons) but no raster image URLs.

backend/app/routers/card_router.py

@@ -51,6 +51,52 @@ async def search_cards_endpoint(
     return {"cached": False, "results": results}
 
 
+@router.get("/sets")
+async def get_sets_endpoint(
+    db: AsyncSession = Depends(mtg_get_db),
+):
+    """
+    Get all sets.
+    """
+    cache_key = "all_sets:all"
+    
+    cached = await cache_get(cache_key)
+    if cached:
+        return {"cached": True, "results": cached}
+    
+    sets = await get_sets(db)
+    
+    # Cache for 1 hour
+    await cache_set(cache_key, str(sets), ttl=3600)
+    
+    return {"cached": False, "results": sets}
+
+
+@router.get("/sets/{set_code}")
+async def get_set_endpoint(
+    set_code: str,
+    db: AsyncSession = Depends(mtg_get_db),
+):
+    """
+    Get a specific set by code.
+    """
+    cache_key = f"set_by_code:{set_code}"
+    
+    cached = await cache_get(cache_key)
+    if cached:
+        return {"cached": True, "results": cached}
+    
+    mtg_set = await get_set_by_code(set_code, db)
+    
+    if not mtg_set:
+        raise HTTPException(status_code=404, detail="Set not found")
+    
+    # Cache for 1 hour
+    await cache_set(cache_key, str(mtg_set), ttl=3600)
+    
+    return {"cached": False, "results": mtg_set}
+
+
 @router.get("/{card_name}")
 async def get_card_endpoint(
     card_name: str,