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/vectors/README.md

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+# sim/vectors — Stimulus Vectors
+
+Deterministic stimulus inputs for directed tests.
+
+Expected layout (populated as subsystem tests land):
+
+- `vectors/memory/` — memory-map probe sequences.
+- `vectors/dmac/` — channel programming sequences.
+- `vectors/gif/` — GIF packet streams (`gsKit`-derived and hand-rolled).
+- `vectors/sif/` — SIF mailbox / DMA sequences.
+- `vectors/ee/` — small EE code payloads used as directed fetch/decode tests.
+- `vectors/iop/` — IOP-side equivalents.
+
+Vectors should be human-readable where practical. Binary blobs must be paired
+with a generator script in `software/tools/` so they can be regenerated.