Package the models on every platform, not just the phone

The Android bundling landed the weights under that platform's asset directory,
which was the wrong home the moment a second packager wanted them. `makepkg -si`
produced a desktop install with no model at all — the same "no face model is
installed" the phone used to show, for the same reason: nothing put the files
anywhere the app looks.

So `models/face/` at the root is the one copy, and both packagers read it:
assemble-apk.sh bundles it as APK assets, and the PKGBUILD installs it to
/usr/share/darkroom/models. Both refuse an LFS pointer rather than shipping a
130-byte file that fails inside the graph loader on a user's machine.

`face_models` now searches three places, most specific first: the account's own
directory, the shared user directory, then $XDG_DATA_DIRS. So a packaged pair is
found automatically and a pair the user placed by hand still outranks it — which
is what keeps a deliberate choice of weights from being overridden by an
upgrade.

$XDG_DATA_DIRS rather than a hard-coded /usr/share: that is the variable a
distribution, a prefix install or a Nix-style store already sets to say where
its data went, and its documented default is exactly the two paths that would
otherwise have been hard-coded. Empty on Android, which has no such directories
— there the APK's copy is unpacked into the shared user directory instead,
because an asset inside a package is not a path anything can read from.

Verified: the APK still carries both models at assets/models/, the PKGBUILD
parses and installs from the new path, 467 tests pass.

Includes the pkgver 0.6.0 → 0.7.0 bump that was already sitting uncommitted in
the working tree.

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

docker/android/README.md

@@ -42,8 +42,8 @@ the runner host's cached registry credentials.
 
 ## Face models
 
-`package.sh` bundles `apps/darkroom-android/android/assets/models/` into the APK, and the entry point
-unpacks it on first launch. **The models are in LFS**, so a clone without `git lfs pull` has 130-byte
+`package.sh` bundles `models/face/` into the APK, and the entry point unpacks it on first launch.
+That directory is shared with the Arch package rather than owned by this platform. **The models are in LFS**, so a clone without `git lfs pull` has 130-byte
 pointers there; the build detects that and stops rather than shipping them.
 
 This exists because Android offers no other route to a model: the directory the app reads from is