docs: link v002.1 architecture, evidence, runbook

[hkimw]

Summary

• Add evidence-gated v002.1 pointer tables to README.md and docs/index.rst.
• Link the architecture explainer draft from pccx PR docs(spec): v002.1 architecture explainer #48, the RTL evidence inventory from pccx-FPGA-NPU-LLM-kv260 PR docs: add sidebar version selector #95, the bitstream runbook from PR Drop EN/KO file-set parity gate (EN-track moves first) #82, and the public project board.
• Keep status language limited to draft, inventory, pre-flight, and planning states.

Validation

• git diff --check
• env PATH=/home/hwkim/Desktop/github/pccxai/pccx/.venv/bin:$PATH make lint
• env PATH=/home/hwkim/Desktop/github/pccxai/pccx/.venv/bin:$PATH make strict
• rg -n "KV260 inference works|Gemma 3N E4B runs on KV260|20 tok/s achieved|timing closed|bitstream ready|production-ready|stable release" README.md docs/index.rst returned no matches

Claim guard

This is link-only documentation. It does not claim KV260 inference, Gemma 3N E4B hardware execution, timing closure, bitstream availability/readiness, achieved throughput, production readiness, or stable release status.

Refs #48
Refs pccxai/pccx-FPGA-NPU-LLM-kv260#95
Refs pccxai/pccx-FPGA-NPU-LLM-kv260#82

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