docs: pin the FGS use case to Local processing > Other

The Console's Local processing options are Media transcoding, Importing/exporting and Other,
not the two-entry list the help page implies, so record which one this app takes and why the
other two are misdeclarations rather than near-misses:

- Media transcoding is converting media into a different format; the scan writes no media file
  at all, it only reads photos to hash and compare them.
- Importing/exporting is moving files in or out of the app; the app's only write is its own
  private hash index, which no other app ever sees - that is also what keeps "nothing leaves
  the device" true.
- Other is described by Play as "specifically user-initiated work and not for regular system or
  server-initiated tasks", which is exactly a scan the user taps Start scan for.

Worth spelling out because a use case that does not match the app is a misdeclaration, and the
description and the accompanying video have to support whichever option is chosen: "reads the
photo library and writes a small local index of file hashes" only fits Other.

docs/PLAY_RELEASE_CHECKLIST.md

@@ -254,10 +254,17 @@ action except the items marked **[code]**.
          > corrupt data; the service stops as soon as the scan finishes or is cancelled, and
          > it is held only for the duration of the scan.
 
-      3. **Use case**: **Local processing: Other** — *"Use for specifically user-initiated work
-         and not for regular system or server-initiated tasks."* The other `dataSync` choices
-         are network transfers (backup/restore, upload/download) and *Local processing: Import
-         or export*, none of which describes a local, user-initiated duplicate scan.
+      3. **Use case**: **Local processing › Other.** The Console puts three options under *Local
+         processing*, and the other two do not describe this app. *Media transcoding* means
+         converting media into a different format — the app writes no media file at all, it only
+         reads photos to hash and compare them. *Importing, exporting* means moving files in or
+         out of the app — the app's only write is its own private index of file hashes, which no
+         other app ever sees. Play's wording for *Other* is *"Use for specifically user-initiated
+         work and not for regular system or server-initiated tasks"*, which is exactly a scan the
+         user taps *Start scan* for. This is not a cosmetic choice: an inaccurate use case is a
+         misdeclaration, and the description and the video have to back up whichever option is
+         picked — "reads the photo library and writes a small local index of file hashes" only
+         fits *Other*.
 
       4. **A link to a video** demonstrating the feature — *"The video should demonstrate the
          steps the user needs to take in your app in order to trigger the feature."* Record it