fix: made the macos app smaller

specs/embedding.allium

@@ -241,7 +241,12 @@ invariant NativeAcceleratedExecution {
     -- On Apple Silicon the model runs on the Apple GPU via EMLX (MLX/Metal,
     -- params placed on the EMLX.Backend GPU device); everywhere else, and as a
     -- fallback when EMLX is unavailable, it runs on optimised native CPU via
-    -- EXLA. Selection is `accelerator: :auto | :emlx | :exla` (default :auto).
+    -- EXLA. Selection is `accelerator: :auto | :emlx | :exla` (default :auto);
+    -- a request for an unavailable backend degrades to the other one.
+    -- Packaged releases ship only the backend their platform can run (runtime:
+    -- conditional deps): macOS releases exclude EXLA, Linux/Windows releases
+    -- exclude the Apple-only EMLX. The selected backend is started on demand
+    -- by the Neural backend, never assumed started at boot.
     -- Neighbour search is HNSW (hnswlib).
 }