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>

packaging/PKGBUILD

@@ -4,7 +4,7 @@
 # makes `makepkg -si` in this directory install what you are actually working
 # on. Swap `source` for a tagged tarball when there is something to release.
 pkgname=darkroom
-pkgver=0.6.0
+pkgver=0.7.0
 pkgrel=1
 pkgdesc="Non-destructive RAW photo library and editor"
 arch=('x86_64')
@@ -43,4 +43,20 @@ package() {
         "${pkgdir}/usr/share/icons/hicolor/256x256/apps/paris.tourolle.darkroom.png"
 
     install -Dm644 "README.md" "${pkgdir}/usr/share/doc/${pkgname}/README.md"
+
+    # The face models, into the last directory the app searches. A pair the
+    # user placed in their own data directory outranks these, so installing
+    # them cannot override a deliberate choice of weights.
+    #
+    # These live in LFS; a checkout without `git lfs pull` has ~130-byte
+    # pointers here. Installing one produces a package whose face indexing
+    # fails inside the graph loader on the user's machine, so refuse instead.
+    for _m in scrfd_500m_640.onnx arcface_mbf_b1.onnx; do
+        _src="models/face/${_m}"
+        if [[ "$(stat -c%s "${_src}")" -lt 100000 ]]; then
+            echo "error: ${_m} is an LFS pointer, not a model — run: git lfs pull" >&2
+            return 1
+        fi
+        install -Dm644 "${_src}" "${pkgdir}/usr/share/darkroom/models/${_m}"
+    done
 }