[docs] flagship polish: discoverability hook, mermaid diagram, BENCHMARKS.md, ROADMAP.md

[peterajhgraham]

Summary

Documentation and discoverability work only — no logic, architecture, or benchmark numbers were changed.

• README hook — four-sentence opening above the existing intro that leads with the scientific motivation (why sub-30 ms p99 for BCI, what makes motor cortex spike trains a hard inference target) before pivoting to what the repo builds.
• Quick Visual — mermaid architecture diagram (renders natively on GitHub) showing spike events → tokenizer → Perceiver cross-attention → self-attention stack → behavior head, with the three Triton kernels annotated at the right layers, and the serving subgraph (scheduler, paged KV cache, FastAPI) on the side.
• Why This Matters Beyond BCI — paragraph after Architecture mapping the engineering patterns to LLM inference systems: continuous batching ↔ vLLM, paged KV cache ↔ PagedAttention, INT8 calibration ↔ LLM.int8(). Makes the repo legible to ML systems engineers who don't know BCI.
• Honest Results callout — GitHub blockquote near the benchmark tables stating the hardware caveat plainly: the work is real and tested, the Triton speedup and full p99 numbers are pending CUDA, and everything is marked rather than estimated.
• BENCHMARKS.md — single consolidated reference with a headline table linking to every per-area report (training, profiling, kernels, quantization, serving), plus per-area sections and a reproduction recipe.
• ROADMAP.md — four scoped next steps (CUDA kernel benchmark sweep on A10, full trial-aligned NLB evaluation + leaderboard, multi-session / cross-subject generalization, end-to-end true INT8 matmul, self-hosted CUDA CI runner).
• CI badge already exists and points at the correct workflow (.github/workflows/ci.yml) — no change needed.

Test plan

• Render README on GitHub; verify the mermaid diagram and Honest Results blockquote render correctly.
• Click every report link in BENCHMARKS.md to confirm paths resolve.
• Set the GitHub repo description and topics from the repo Settings page (see chat for the exact strings — the MCP toolset available in this session does not expose repo-metadata mutations).

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