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, by the app's rule.
src/clip-keywords.ts applies the rule. src/clip-keyword-vectors.ts holds the
16 categories from Ente's discover.json with the text embedding Ente's CLIP
text model gives each query. bin/clip-keyword-vectors writes that file and the
test fixture in a digest-pinned Python image, with every download pinned by
sha256; it runs by hand only. quak gains no dependency.

Model: opus-5-5

src/backup.ts

@@ -14,9 +14,9 @@
 //         YYYY/YYYY-MM/YYYY-MM-DD/
 //             YYYY-MM-DD.<fileID>.<ext>    the decrypted bytes (the save path)
 //             YYYY-MM-DD.<fileID>.json     per-file metadata sidecar, with
-//                                          the file's ML data and its
-//                                          original's EXIF, XMP and
-//                                          dimensions
+//                                          the file's ML data, its
+//                                          keywords, and its original's
+//                                          EXIF, XMP and dimensions
 //         collections/<name>/<title>       symlink to the original
 //         collections/<name>.json          per-collection metadata
 //         account.json                     the account's email and user ID
@@ -77,6 +77,7 @@ import { readFile } from "node:fs/promises";
 import { dirname, extname, join, relative, resolve } from "node:path";
 import lockfile from "proper-lockfile";
 
+import { clipKeywords } from "./clip-keywords.js";
 import { removeLeftoverTempFiles } from "./download/index.js";
 import { describeError } from "./errors.js";
 import {
@@ -497,8 +498,9 @@ const imageMetadataFor = async (
     }
 };
 
-// The file's JSON: its basic fields, its magic metadata, its ML data or the
-// reason the ML data is missing, and its image metadata.
+// The file's JSON: its basic fields, its magic metadata, its ML data without
+// the CLIP embedding and the keywords that embedding gives, or the reason the
+// ML data is missing, and its image metadata.
 const writeSidecar = (
     path: string,
     file: EnteFile,
@@ -514,7 +516,13 @@ const writeSidecar = (
     };
     if (file.magicMetadata) meta.magicMetadata = file.magicMetadata;
     if (file.pubMagicMetadata) meta.pubMagicMetadata = file.pubMagicMetadata;
-    if (ml.mlData) meta.mlData = ml.mlData;
+    if (ml.mlData) {
+        const { clip: _clip, ...mlDataWithoutClip } = ml.mlData;
+        meta.mlData = mlDataWithoutClip;
+        const isVideo = file.metadata.fileType === "video";
+        const keywords = clipKeywords(ml.mlData, isVideo);
+        if (keywords) meta.keywords = keywords;
+    }
     if (ml.mlDataError) meta.mlDataError = ml.mlDataError;
     if (image.imageMetadata) meta.imageMetadata = image.imageMetadata;
     if (image.imageMetadataError) {