Expose --xmp-sidecar flag via config

[laforcem]

Picks up #775.

Changes

This PR exposes icloud_photos_downloader's --xmp-sidecar flag as a new config variable: xmp_sidecar. The default setting is false.

A sidecar file will look something like this:

<?xml version='1.0' encoding='utf-8'?>
<x:xml_doc xmlns:x="adobe:ns:meta/" x:xmptk="icloudpd 1.32.3+2035bb1">
  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
    <rdf:Description rdf:about="" xmlns:dc="http://purl.org/dc/elements/1.1/">
      <dc:description>Screenshot</dc:description>
    </rdf:Description>
    <rdf:Description rdf:about="" xmlns:Iptc4xmpExt="http://iptc.org/std/Iptc4xmpExt/2008-02-29/">
      <Iptc4xmpExt:DigitalSourceType>screenCapture</Iptc4xmpExt:DigitalSourceType>
    </rdf:Description>
    <rdf:Description rdf:about="" xmlns:photoshop="http://ns.adobe.com/photoshop/1.0/">
      <photoshop:DateCreated>2026-06-30T12:24:53-0500</photoshop:DateCreated>
    </rdf:Description>
    <rdf:Description rdf:about="" xmlns:tiff="http://ns.adobe.com/tiff/1.0/">
      <tiff:Make>Screenshot</tiff:Make>
    </rdf:Description>
    <rdf:Description rdf:about="" xmlns:xmp="http://ns.adobe.com/xap/1.0/">
      <xmp:CreateDate>2026-06-30T12:24:53-0500</xmp:CreateDate>
    </rdf:Description>
  </rdf:RDF>
</x:xml_doc>

Behavior

Retroactive backfill

If files are already downloaded while the flag is false, then it is later turned to true, .xmp sidecar files will be downloaded for all files already in the library. Critically, this does not re-download assets already downloaded; just the sidecars.

Live Photos

While Live Photos already have two files downloaded for each (.HEIC + .MOV), only one .xmp sidecar is downloaded for one Live Photo. The sidecar counts for both files.

Deletion

When assets are deleted from iCloud, icloudpd will sync those deletions down to the sidecar as well, leaving no orphaned .xmp files.

---

Let me know if any changes are desired here.

[roleme]

Been running this and it works great — thanks for picking it up. With xmp_sidecar=true every photo gets its .xmp alongside it, and importantly the sidecar carries the GPS that Apple keeps catalog-side (so photos with no GPS in the file itself finally get a location downstream). Immich picks the sidecar up automatically, which was exactly what I was after.

One heads-up in case it helps: icloudpd itself crashes if --xmp-sidecar and --only-print-filenames ever run together (it tries to write the .xmp into a folder that print-mode never created → FileNotFoundError in xmp_sidecar.py). This PR is fine because the flag only goes on the sync command, and check_files() builds its own --only-print-filenames command separately. Just worth a one-line comment there so nobody later "tidies up" check_files() to reuse command_line_builder() and accidentally reintroduces the crash. I've filed the underlying bug upstream too.