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/phase0_checklist.md

@@ -0,0 +1,43 @@
+# Phase 0 Checklist
+
+This is the architecture-lock checklist to complete before substantial RTL work.
+
+Decision records under `docs/decisions/` are the source of truth for locked
+choices. This checklist is now a progress/navigation view.
+
+## Locked decisions
+
+- [x] Posture — locked: staged subset on current hardware — see
+  `docs/decisions/0001-posture.md`
+- [x] BIOS policy — locked: real BIOS plus narrow debug stubs — see
+  `docs/decisions/0002-bios-policy.md`
+- [x] Golden reference strategy — locked: multiple references with role
+  separation — see `docs/decisions/0003-golden-reference.md`
+- [x] First visible milestone — locked: split platform/video proof and
+  EE/BIOS trace proof — see
+  `docs/decisions/0004-first-visible-milestone.md`
+- [x] Trace format — locked: common text envelope plus subsystem-specific
+  payloads — see `docs/decisions/0000-trace-format.md`
+
+## Still to lock
+
+- [ ] Memory architecture policy
+- [ ] Media/storage policy
+- [ ] Validation posture beyond the initial trace-format choice
+
+## Required documents
+
+- `docs/contracts/memory.md`
+- `docs/contracts/ee.md`
+- `docs/contracts/intc.md`
+- `docs/contracts/dmac.md`
+- `docs/contracts/gif_gs.md`
+- `docs/contracts/sif.md`
+- `docs/contracts/validation.md`
+
+## Exit criteria for Phase 0
+
+- Major subsystem ownership is written down.
+- The memory and DMA contracts are explicit enough to build stubs.
+- The first three milestones are named and measurable.
+- The team agrees on what is allowed to be stubbed in Phase 1.