feat: Import Lightroom XMP sidecars

[StephenMasseur]

Summary

• Add Lightroom XMP adjustment import for individual images
• Add folder-level import for matching .xmp sidecars by filename
• Support attribute and element-style crs:* XMP adjustment values
• Document single-image and folder sidecar import workflows in the README

Testing

• npm run build
• cargo fmt --check
• cargo test
• git diff --check

[StephenMasseur]

You can right-click an image to select individual .xmp, or right click on folder in left bar then click "Import Sidecar XMP" for it to import all .xmps with matching filenames from the folder containing the content.