docs(readme): lead with what it does and the quickstart; reference moves to docs/

[askalf]

Docs only. The README leads with what cordon does and how to run it, and the reference material moves to docs/.

Top screen: the one-line pitch, the redaction diagram, and a three-line docker run quickstart with the base-URL change and the X-Redacted headers as proof. Next come what it catches, how it behaves (fail closed, the three modes, audit, tenant policy, signed releases) and what it does not do.

Moved verbatim, nothing deleted:

• docs/reference.md: the full captured round trip (both clients, the response headers, what the provider was sent, the audit line), audit format and verification, per-tenant policy, ops endpoints, configuration.
• docs/deploy.md: compose, deploy.sh, attestation verification, the dario integration link.
• docs/development.md: running from source and what each test suite proves.

All three are linked from a Reference list. README: 169 → 74 lines. Every relative link resolves; npm run typecheck and npm test are green.

[sprayberry-redline]

Deterministic approval — no LLM reviewed this diff.

Classified low-risk: docs-only (4 file(s)).

This repository requires an approving review before auto-merge can proceed, so this
approval exists to satisfy that gate without spending a full Code Reviewer execution
on a diff whose risk is provable from the file list alone. This approval satisfies ONLY
the review requirement — the merge still separately requires green CI, which this sweep
does not and cannot short-circuit.

Anything outside the docs allowlist, any major dependency bump, any non-Dependabot
dependency change, and any unknown diff keep the full reviewer path.