build(mac): establish LÖVE 12 Metal parity

mobile/macos/APPLE_DEPENDENCIES_REF

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+a5522634f1e581a1ebab73bf3ab4bd7a853b7a3e

mobile/macos/LOVE_SOURCE_REF

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+97d4465e8c81099f79696ea4b4bb8b1f9083bc1a

mobile/macos/LOVE_VERSION

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+12.0

mobile/macos/README.md

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+# macOS build
+
+The desktop app uses the pinned LÖVE 12 runtime built from the LÖVE source
+tree and the matching Apple dependency repository. The runtime enables Metal
+and is fused into the branded `gen1recomp++.app` bundle.
+
+Build the runtime and desktop app from the repository root:
+
+```bash
+scripts/build_love_macos.sh --fetch
+LOVE_APP="$PWD/.bazinga/love12/love.app" scripts/build.sh mac --no-notarize --identity -
+```
+
+The source and dependency revisions are recorded in `LOVE_SOURCE_REF` and
+`APPLE_DEPENDENCIES_REF`. Delete `.bazinga/love12/source` or use `--clean`
+when changing those pins.
+
+The packaged executable is `gen1recomp++` inside `gen1recomp++.app`, and the
+bundle declares LÖVE 12.0 compatibility.