Documentation overhaul + examples

## Summary
Split docs into a small docs site with quickstarts, configuration reference, API reference, and an ops guide (metrics/pprof).

## Motivation
- Faster onboarding
- Clear runbooks for operating at scale

## Scope
- `/docs` with mkdocs or mdBook
- Quickstart: local & Docker/Tor
- Example: crawl a tiny local site; Prometheus+Grafana sample dashboard
- Architecture diagrams

## Acceptance Criteria
- A new user can run a crawl and see metrics in <10 minutes
- README becomes a short entry point linking to docs

## Tasks
- [ ] Create docs framework and structure
- [ ] Add examples and diagrams
- [ ] Update README to point to docs