docs: reconcile OXC/Rust roadmap with completed evidence

[swernerx]

Summary

• mark RFC 0001 accepted and update its delivery phases to reflect the completed protocol, corpus, and internal OXC/Rust reference path
• link the measured spike from RFC 0001 and the ADR index, and record the current migration decision
• remove the stale downstream-project dependency language
• make primitive/literal Rust type-record construction explicit as the next candidate while keeping the TypeScript 7 Go checker authoritative
• clarify the repository overview and evidence index without changing source code or the producer protocol

Boundary

The Rust/OXC layer remains an internal reference and migration harness. The recorded spike does not establish compiler equivalence, production readiness, or a performance advantage, and no semantic category is approved for replacement.

Validation

• DPRINT_CACHE_DIR=/tmp/dprint-cache-issue39 npx hereby check:format — passed
• git diff --check — passed
• changed-Markdown relative-link validation — passed (5 files)
• repository scope check — passed; all changed paths are Markdown
• stale downstream reference check — passed; no Palamedes references remain in project Markdown

Closes #39