Refactor opcode metadata ownership

THIRD_PARTY_NOTICES.md

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+# Third-party notices and research acknowledgments
+
+This file records incorporated third-party code and prior public research that materially informed this
+project. It does not license Eushully game assets or code, and no original game files are distributed with
+this repository.
+
+## Eushully-Decompiler research
+
+Early SYS4 instruction decoding and the initial opcode ABI/catalog were informed by Kelebek's public
+[Eushully-Decompiler](https://github.com/Kelebek1/Eushully-Decompiler) project. That work established a
+valuable starting point and accelerated this reimplementation. Historical and per-opcode provenance is
+preserved in `vm-map/opcodes.toml`.
+
+This repository does not vendor the upstream source files. Its opcode registry combines that foundational
+catalog with independent script-corpus analysis, native `AGE.EXE` investigation, runtime probes, and
+reimplementation testing. This acknowledgment is not a claim that the project was developed under a formal
+clean-room process.
+
+## GARbro AGF decoding algorithm
+
+`engine/Age.Engine/Sys4/AgfDecoder.cs` ports the AGF decoding algorithm from GARbro's
+`ArcFormats/Eushully/ImageAGF.cs`, Copyright (c) 2014-2020 morkt, under the MIT License:
+
+> Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
+> associated documentation files (the "Software"), to deal in the Software without restriction, including
+> without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+> copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the
+> following conditions:
+>
+> The above copyright notice and this permission notice shall be included in all copies or substantial
+> portions of the Software.
+>
+> THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
+> LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO
+> EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+> IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+> USE OR OTHER DEALINGS IN THE SOFTWARE.