docs: readme

[jithinraj]

Summary

Top-fold clarity improvement plus a final README polish. The headline uses "signed action records" (the developer-clear hook); the next paragraph defines the formal artifact as "portable signed interaction records" (the protocol-grade term covering decisions, observations, denials, payment events, provisioning events, gateway reports, and bundles). Present-tense framing; the canonical line "Record locally. Verify across boundaries." is unchanged.

Scope (README.md only)

• New opening paragraphs (headline, present-tense context, formal definition).
• Quickstart fix: the failure object exposes code and message (there is no reason field); the example no longer throws dead fallback text.
• The MCP gateway records recipe is now discoverable: a Use-cases row, a Try-it entry running the example demo and tamper checks, and a start link in the Choose-your-path gateway row.
• Badges, the "What PEAC records" table content, boundary language, and all command conventions (npm install for libraries, pnpm dlx for one-off CLI, npx -y for the MCP server) are unchanged.
• No protocol behavior changes; no package, version, or schema changes.

Validation

• prettier clean; git diff --check clean; tooling suite 955 passed (37 files); public-artifact and planning-leak scanners pass.
• Both documented demo commands verified end-to-end from the workspace root.