docs: advertise tools/rdna/serve_rdna.sh + wiki

[BlivionIaG]

Why

#vllm-rdna (Oct 10): newcomers were missing the in-tree launch path because the stock upstream README never mentions it. Agents then invent broken Docker/vllm serve lines.

What

• README.md: an RDNA fork banner at the top. It covers bash tools/rdna/serve_rdna.sh RECIPE=…, the full recipe list (flashnext, flashnext-mtp0, flashnext-mtp2, flashnext-pp3, flashnext-pp3-mtp2, 27b-awq, 27b-exl3, dsv4-flash, full), the PRINT=1 dry-run, EXTRA_ARGS (e.g. --monokernel) and the wiki link. A one-line RDNA pointer is added under "Getting Started".
• AGENTS.md: a new "0. RDNA fork (read first)" section on top of the unchanged upstream file:
  • launcher and recipes;
  • PLE modes;
  • common mistakes (breakable cudagraph env, BF16, AITER/CK);
  • RDNA code rules: arch gating, FP16/Wave32, current-stream HIP launches, no wvSplitK/LLMM1 on gfx10, registry kernel disabling, cudagraph correctness + A/B, four-metric bench reports;
  • where the RDNA docs live.
• Upstream's contribution policy, uv workflow, test and lint guidance and commit trailers are kept. Two fork additions:
  • duplicate-work checks against opengfx1030/vllm-rdna, backlog drafts included;
  • a note that the precompiled artifacts are CUDA builds, so RDNA builds the ROCm extensions from source.

Changes since the first version

• Rebased on rdna_extras @ 1c1426d585 (was 102 commits behind).
• AGENTS.md is no longer replaced; upstream sections stay so upstream syncs don't conflict.
• Dropped the stale rdna_extra/v0.31.0 pointer: rdna_extras is v0.31 since [RDNA2] Port rdna_extras onto vLLM v0.31.0 (rdna_extra/v0.31.0) #47.
• Dropped the VLLM_RDNA_FUSED_HC and VLLM_PLE_QUANT_DIR "mistakes": no recipe sets them now. PLE is documented through the launcher's PLE= switch instead.
• Added the PP3 and full recipes and EXTRA_ARGS.
• Added the RDNA code rules block for agents changing code.

Out of scope

No runtime, recipe or kernel changes. Wiki updates land separately in BlivionIaG/gfx1030-wiki.

Please leave draft

Human pass before merge: this is the first thing GitHub shows on the fork.