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/tb/integration/README.md

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+# sim/tb/integration
+
+Cross-subsystem integration testbenches that exercise full pipelines end to
+end. Distinct from the per-subsystem testbenches in sibling `tb/<subsys>/`
+directories — those prove one block in isolation; these prove a chain.
+
+## Wave 2 contents
+
+- `tb_bgcolor_via_dma.sv` — "programmable BGCOLOR via DMA/GIF" (Milestone A+).
+  Chain: `dmac_reg_stub → gif_path_stub → gs_stub → platform_video_stub`
+  with four trace sinks. Configures DMAC channel 2, provides a one-qword
+  project-local packet carrying a BGCOLOR register write, verifies the
+  color propagates through to the raster output.
+
+See `docs/wave2_dma_gif_plan.md` for the Wave 2 scope and the packet format.