[Shillerxorg]

…age caching

• Nginx proxy cache: add a dedicated 1GB disk cache zone in frontend nginx for /api/images/ with proxy_cache_lock to prevent redundant multi-hop transfers between frontend, backend, and PostgreSQL.
• Backend HTTP cache headers: send Cache-Control with immutable 30-day max-age and ETag for official card and set images, and 1-hour must-revalidate for custom cards. Return 304 Not Modified on matching If-None-Match.
• Frontend image loading: preserve native lazy loading in CardImage without forcing eager loading when entering the viewport margin.
• Database: avoid passing pool arguments to create_engine when running tests against SQLite.
• Tests: add comprehensive unit tests in test_image_cache_headers.py covering 200 headers, 304 responses, weak ETags, and custom card caching.

What and why

Validation

• Relevant automated checks pass
• Documentation was updated when behavior changed

Card UI (when applicable)

• I checked docs/CARD_SYSTEM.md and followed the established card visual language where it fits
• I included desktop/mobile screenshots or explained why they are not relevant
• If this introduces a genuinely new visual idea, I explained why the existing patterns do not fit