docs: open-source README overhaul + CONTRIBUTING guide — welcoming PRs

feat: add GoatCounter + server-side analytics middleware + /stats page

deploy: add fly.toml + update Dockerfile for Fly.io (Sydney region)

content: sync enriched modules 1-10 from workspace

content: modules 5-7 (skills, security, config) — 10 lessons

content: modules 8-10 (extending, deployment, case study) — 9 lessons

Initial public release: OpenClaw Academy