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>

docs/decisions/README.md

@@ -0,0 +1,22 @@
+# Design Decisions
+
+This directory is for short decision records once the team starts locking items.
+
+Suggested format:
+
+- title
+- date
+- status
+- context
+- options considered
+- decision
+- consequences
+
+Locked so far:
+
+- `0000-trace-format.md`
+- `0001-posture.md`
+- `0002-bios-policy.md`
+- `0003-golden-reference.md`
+- `0004-first-visible-milestone.md`
+- `0005-phase0-source-of-truth.md`