Add Steam library import via OpenID

- Steam OpenID flow: user authenticates with Steam, we get their Steam ID
- Server-side API key fetches their owned games with playtime
- Import page shows full library, marks already-imported games
- Imported games land in backlog as GAMES items with hours_played set
- STEAM_API_KEY env var plumbed into both prod and dev containers

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

kboris/settings.py

@@ -5,6 +5,7 @@ BASE_DIR = Path(__file__).resolve().parent.parent
 
 SECRET_KEY = os.environ.get('DJANGO_SECRET_KEY', 'dev-insecure-key')
 DEBUG = os.environ.get('DEBUG', 'False').lower() == 'true'
+STEAM_API_KEY = os.environ.get('STEAM_API_KEY', '')
 
 ALLOWED_HOSTS = [
     'k-boris.tech',