Untag FR-CAT-13, which no XMP is read or written to satisfy

FR-CAT-13 asks for standard XMP sidecars read and written — ratings, colour
labels, keywords and hierarchical subjects, title, description, copyright, GPS,
in `xmp:`/`dc:`/`lr:` schemas — so that other tools interoperate. Its one tag
was the module header of `dr-catalog/src/keywords.rs`.

That module stores keywords in SQLite. It names `dc:subject` twice, both times
in prose explaining why a keyword's text is the fact rather than its row id,
which is a good reason to have written it that way and not evidence of an XMP
implementation. Nothing in the tree parses or emits XMP: `dr-export`'s metadata
module writes EXIF and says in its own header that IPTC and XMP are named by
FR-EXP-8 and neither is read.

`dr-preset-xmp` is the crate whose name most invites the mistake. It reads
Lightroom `.xmp` *presets* — develop settings — under FR-DEV-6, and knows
nothing about the metadata schemas FR-CAT-13 is about.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/outstanding.md

@@ -277,11 +277,14 @@ well optimised — ETag pruning under FR-NC-4 turns an unchanged 50k library int
 gap is narrower than it reads. It is the *first* build against a large remote library that pays, and
 that is the moment a new user meets.
 
-**FR-CAT-13 — XMP interoperability, tagged and not met.** Read and write standard XMP sidecars. The
-single tag sits on `keywords.rs`, which stores keywords; no XMP is parsed or written anywhere in the
-tree, and `dr-export`'s metadata module says so about its own half ("neither is read by `dr-decode`
-today"). Listed here rather than silently, because a tag makes a gap invisible and this one is
-load-bearing for interoperating with the editors FR-CAT-14 imports from.
+**FR-CAT-13 — XMP interoperability, untagged and not met.** Read and write standard XMP sidecars.
+Its single tag sat on `keywords.rs`, which stores keywords in the catalog and mentions `dc:subject`
+in a comment about what a keyword's text is *for*; no XMP is parsed or written anywhere in the tree,
+and `dr-export`'s metadata module says so about its own half ("neither is read by `dr-decode`
+today"). The tag has been removed — `dr-preset-xmp` is not the counter-example it looks like, being
+a reader of Lightroom *presets* under FR-DEV-6, which is a different file and a different purpose.
+Listed here rather than silently, because a tag makes a gap invisible and this one is load-bearing
+for interoperating with the editors FR-CAT-14 imports from.
 
 ---