docs: document App Attest protocol 3
Document device-bound renewable sessions
Document PumpSync component versioning policy
docs: split Self-Hosting-and-Demo into two pages, self-hosting first Self-hosting (real Tandem account) and demo mode (no Tandem account) are different audiences with different setup steps; bundling them into one page buried the self-host walkthrough under demo instructions. Splits into Self-Hosting.md (presented first) and Demo-Mode.md, each linking to the other, and rewrites the physical-iPhone reverse-proxy section to state only the PumpSync-specific facts plus links to well-maintained self-hosted options (Nginx Proxy Manager, Caddy, Traefik) rather than documenting reverse-proxy setup itself. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>