Add content-based hashing to recipe images for proper cache invalidation
while maintaining graceful degradation through dual file storage.
Changes:
- Add imageHash utility with SHA-256 content hashing (8-char)
- Update Recipe model to store hashed filenames in images[0].mediapath
- Modify image upload endpoint to save both hashed and unhashed versions
- Update frontend components to use images[0].mediapath with fallback
- Add migration endpoint to hash existing images (production-only)
- Update image delete/rename endpoints to handle both file versions
Images are now stored as:
- recipe.a1b2c3d4.webp (hashed, cached forever)
- recipe.webp (unhashed, graceful degradation fallback)
Database stores hashed filename for cache busting, while unhashed
version remains on disk for backward compatibility and manual uploads.
