Probe and compile for a package's models, not only the user's

`inference::init` listed the models from the user's shared directory
alone, while the app loads them from there or from the package's
`/usr/share/darkroom/models`. On a fresh package install the probe found
"no model to probe with", stayed on the CPU, and compiled nothing. Both
now resolve each file with the same search, `library::shared_model`.

The PKGBUILD names the ONNX Runtime packages as optional dependencies,
since the app loads one from /usr/lib if present.

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

packaging/PKGBUILD

@@ -16,8 +16,13 @@ license=('GPL-3.0-or-later')
 # Nextcloud credentials (FR-NC-2) — gnome-keyring or kwallet both provide it.
 depends=('vulkan-icd-loader' 'fontconfig' 'libxkbcommon')
 makedepends=('cargo' 'git')
+# ONNX Runtime is loaded from /usr/lib at launch if a package put it there
+# (docs/inference.md §3): the CPU build is 8–10× the built-in tract, the
+# ROCm build adds the MIGraphX rung on an AMD GPU. Neither is required.
 optdepends=('gnome-keyring: store Nextcloud credentials'
-            'kwallet: store Nextcloud credentials')
+            'kwallet: store Nextcloud credentials'
+            'onnxruntime-cpu: run the neural models on every core'
+            'onnxruntime-rocm: run the neural models on an AMD GPU')
 options=('!lto')  # the workspace sets its own LTO in Cargo.toml
 
 _repo="$(cd "${startdir}/.." && pwd)"