Initial commit: retroDE_ps2 — first-of-its-kind PS2 GS FPGA core (DE25-Nano / Agilex 5)

RTL (GS rasterizer, EE core stub, platform bridge, LPDDR4B path), sim regression
(272 TBs), docs, and tooling. Copyrighted PS2 content (BIOS, game code, GS dumps,
and all dump-derived textures/traces) is excluded via .gitignore and stays local.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

references/supplemental/README.md

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+# Supplemental References (Claude pass)
+
+These notes supplement the top-level `references/` files produced by the Codex
+pass. Goal: add sources Codex did not surface, without duplicating its memory
+map / workstream / emulator-landscape work.
+
+Files in this folder:
+
+- `sony_official_docs.md`: primary Sony register manuals for GS and the VUs.
+  Codex leaned on `ps2tek` (community-compiled); these are one layer closer to
+  the silicon.
+- `fpga_prior_art.md`: PSX-on-FPGA projects. None are PS2, but they are the
+  closest real-world methodology templates for a console-gen FPGA effort.
+- `architecture_studies.md`: high-level architecture writeups, an academic
+  VU-on-FPGA feasibility thesis, and MiSTer community consensus on why PS2
+  has not been attempted.
+- `source_log.md`: sources introduced in this pass, with URLs and short notes.
+
+These are reference-only. No implementation claims, no planning overrides —
+Codex's `implementation_workstreams.md` remains the planning map.