Publish Chimera GFX source

adapters/retroarch/README.md

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+# RetroArch adapter boundary
+
+The compiled scaffold exposes a dependency-free query contract. It reports
+RGUI and SDL software fallback as the intended integration path, but reports
+software-frame binding not yet implemented and hardware contexts unavailable.
+Every hardware-context request returns `SAFETY_POLICY`.
+
+The future driver lifecycle is: initialize a `chimera_gfx_context`, create one
+surface, create/reuse textures for software core frames, upload a frame, present
+through the selected backend, then destroy texture, surface, and context in
+that order. No RetroArch private type or header enters the public library API.