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>

sim/data/ch56_test_image_4w.mem

@@ -0,0 +1,7 @@
+// Ch56 external-mode unit-TB image (4 words, one per line)
+// Chosen to be maximally distinguishable from the built-in Ch54 image
+// so a byte-compare mismatch would be unambiguous.
+deadbeef
+cafebabe
+12345678
+87654321