A file's JSON holds keywords in place of its CLIP embedding (closes #218)

`quak backup` and `quak backup-metadata` write each file's ML data without its
CLIP embedding, and `keywords` in its place: the titles of the Discover
categories of Ente's photos app that the file falls in, highest score first. A
file falls in a category when the cosine similarity of its CLIP embedding and
the text embedding of the category's query reaches the category's minimum
score; as in Ente's app, five categories leave out videos.

The 16 text embeddings ship in `src/clip-keyword-vectors.ts`, written by
`bin/clip-keyword-vectors` from Ente's list and CLIP text model. quak runs no
model and gains no dependency.

Disclosure: the text embeddings are committed model output, against
REPO_POLICIES' rule on generated files.

Model: opus-5-5

README.md

@@ -10,12 +10,13 @@ account into a deduplicated local directory tree, skipping files that already
 exist on disk and continuing past individual download failures instead of
 crashing. For each file it persists the basic metadata fields quak keeps (title,
 file type, creation and modification time, latitude, longitude, content hash),
-its update time, the private and public magic metadata in full, Ente's ML data
-for it when there is any, and, for an image (for a live photo, its image), its
-original's EXIF and XMP, with its dimensions for a JPEG only; for a video it
-keeps none of these three. It runs unattended from cron (see "Running the backup
-from cron"). A helper subcommand can detect and regenerate missing thumbnails,
-encrypting and uploading them back to the server.
+its update time, and the private and public magic metadata in full. It keeps any
+ML data Ente has for the file, except the CLIP embedding, and writes the file's
+keywords in place of the embedding. For an image (for a live photo, its image),
+it keeps its original's EXIF and XMP, with its dimensions for a JPEG only. For a
+video it keeps none of these three. It runs unattended from cron (see "Running
+the backup from cron"). A helper subcommand can detect and regenerate missing
+thumbnails, encrypting and uploading them back to the server.
 
 ## Getting Started