README and architecture documentation

[troyscott]

Description

Write comprehensive README.md and architecture docs for the open-source project.

README sections

• Project overview and motivation
• Architecture diagram (Mermaid)
• Prerequisites (az CLI, Tailscale account, Azure subscription)
• Quick start (3 commands: clone, configure, make up)
• Cost breakdown (~$20/mo for full dev environment)
• Configuration reference
• Contributing guide link

Docs

• docs/architecture.md — detailed architecture with diagrams
• docs/tailscale-setup.md — Tailscale account + client setup guide
• docs/cost-breakdown.md — itemized monthly costs

Acceptance criteria

• README enables someone to go from zero to running in 15 minutes
• Architecture diagram shows all components and data flow
• Cost breakdown is accurate and up-to-date
• Tailscale setup covers free tier signup through first connection