Split the dense README into focused docs

[collinsadi]

The root README.md (around 227 lines) packs the quick-start, architecture, command reference, and privacy statement into one page, which makes it hard to scan. We should extract docs/ARCHITECTURE.md and docs/DEPLOYMENT_GUIDE.md, leaving the README as a concise overview with links.

Acceptance criteria

• The architecture and deployment content is moved to docs/ and linked from the README.
• The README stays a focused entry point.