fix(media-use): tests never write into the person's media library (#4459)

* fix(media-use): tests never write into the person's media library

* fix(media-use): guard the media home only in this repo's test runs

* test(media-use): probe the media home from a plain child process

* fix(media-use): keep miss logging best-effort when home is unresolvable

* test(media-use): miss logging survives an unresolvable media home

* docs(media-use): describe the media library without naming an app

* chore(media-use): refresh the skills manifest hash

scripts/check-media-use-copy-parity.test.mjs

@@ -15,6 +15,7 @@ export const MEDIA_USE_COPY_NAMES = [
   "index-gen.mjs",
   "manifest.mjs",
   "media-fetch.mjs",
+  "media-home.mjs",
   "npx-sync.mjs",
   "parakeet-words.mjs",
   "prefs-store.mjs",