docs: simplify README for npm install

[cafitac]

Summary

• Replace the long operator-heavy README with a short OSS-facing README.
• Keep the npm global install path as the primary setup path.
• Keep only a minimal one-shot npm usage example, a basic memory example, Hermes note, local-first privacy note, and links to deeper docs.

Verification

• git diff --check
• npm exec --yes --package @cafitac/agent-memory@0.1.155 -- agent-memory doctor