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/services/mtgjson_downloader.py

@@ -0,0 +1,137 @@
+#!/usr/bin/env python3
+"""
+MTGJSON Data Downloader
+
+Downloads all MTGJSON data files and stores them for import.
+"""
+
+import gzip
+import json
+import os
+import sys
+from pathlib import Path
+from urllib.request import urlretrieve
+from urllib.parse import urljoin
+
+# MTGJSON API v5 base URL
+MTGJSON_API_V5 = "https://mtgjson.com/api/v5"
+
+# Files to download with their types
+MTGJSON_FILES = {
+    "AllPrintings.psql.gz": {
+        "name": "AllPrintings",
+        "description": "Main cards database (PSQL format)",
+        "type": "psql",
+    },
+    "AllSetFiles.zip": {
+        "name": "AllSetFiles",
+        "description": "Set and card data",
+        "type": "zip",
+    },
+    "AllDeckFiles.zip": {
+        "name": "AllDeckFiles",
+        "description": "Deck data",
+        "type": "zip",
+    },
+    "AllIdentifiers.json.gz": {
+        "name": "AllIdentifiers",
+        "description": "Card identifiers",
+        "type": "json",
+    },
+    "CardTypes.json.gz": {
+        "name": "CardTypes",
+        "description": "Card types",
+        "type": "json",
+    },
+    "DeckList.json.gz": {
+        "name": "DeckList",
+        "description": "Deck list metadata",
+        "type": "json",
+    },
+    "Keywords.json.gz": {
+        "name": "Keywords",
+        "description": "Card keywords",
+        "type": "json",
+    },
+    "SetList.json.gz": {
+        "name": "SetList",
+        "description": "Set list metadata",
+        "type": "json",
+    },
+}
+
+
+def get_downloads_dir() -> Path:
+    """Get the downloads directory path."""
+    data_dir = Path(os.environ.get("MTGDATA_DIR", "/app/data"))
+    downloads_dir = data_dir / "mtgjson" / "downloads"
+    downloads_dir.mkdir(parents=True, exist_ok=True)
+    return downloads_dir
+
+
+def download_file(url: str, destination: Path) -> bool:
+    """Download a file from URL to destination."""
+    try:
+        print(f"Downloading {url}...")
+        urlretrieve(url, destination)
+        size_mb = destination.stat().st_size / (1024 * 1024)
+        print(f"  ✓ Downloaded to {destination} ({size_mb:.1f} MB)")
+        return True
+    except Exception as e:
+        print(f"  ✗ Failed to download {url}: {e}")
+        return False
+
+
+def download_all_files() -> list[Path]:
+    """Download all MTGJSON files."""
+    downloads_dir = get_downloads_dir()
+    downloaded_files = []
+    
+    print("=== MTGJSON Data Download ===\n")
+    
+    for filename, file_info in MTGJSON_FILES.items():
+        url = urljoin(MTGJSON_API_V5, filename)
+        destination = downloads_dir / filename
+        
+        if download_file(url, destination):
+            downloaded_files.append(destination)
+        else:
+            print(f"  ⚠ Continuing with downloaded files only")
+    
+    print(f"\n=== Download Complete ===")
+    print(f"Downloaded {len(downloaded_files)} files to {downloads_dir}")
+    return downloaded_files
+
+
+def verify_downloads(downloaded_files: list[Path]) -> bool:
+    """Verify all expected files are downloaded."""
+    print("\n=== Verifying Downloads ===\n")
+    
+    all_ok = True
+    for filename, file_info in MTGJSON_FILES.items():
+        filepath = Path(get_downloads_dir() / filename)
+        if filepath.exists():
+            size_mb = filepath.stat().st_size / (1024 * 1024)
+            print(f"✓ {filename:30} ({size_mb:.1f} MB)")
+        else:
+            print(f"✗ {filename:30} (MISSING)")
+            all_ok = False
+    
+    if all_ok:
+        print("\n✓ All files downloaded successfully")
+    else:
+        print("\n⚠ Some files are missing")
+    
+    return all_ok
+
+
+def get_file_list() -> list[Path]:
+    """Get list of all downloaded files."""
+    downloads_dir = get_downloads_dir()
+    files = [downloads_dir / filename for filename in MTGJSON_FILES.keys()]
+    return [f for f in files if f.exists()]
+
+
+if __name__ == "__main__":
+    downloaded = download_all_files()
+    verify_downloads(downloaded)