docs(site): sync RSR/privacy/cookbook docs, add contributing guide - #7

What

Brings the documentation site up to date with everything shipped in PRs #2-#6, and adds a Development section with a contribution guide. Website-only change (per repo rules, no product files touched).

Why

The docs site predated the recent work: RSR metric, privacy positioning, LangGraph/CrewAI cookbooks, and the contribution process existed only in the README/repo root. Roadmap WS-J spirit - keep /docs matching the product.

How

Updated pages

• Divergence Metrics: new Recovery Step Ratio (RSR) section (window semantics, ratio math, fallback rule).
• Regression Gates: max_recovery_step_ratio in the assertion example; --max-recovery-ratio row (opt-in) in the CLI table.
• Reading the Report: recovery line in the terminal sample + recovery finding in --explain output.
• Configuration: max_recovery_ratio / max_recovery_step_ratio keys in the TOML example.
• Introduction: framework coverage (LangGraph/CrewAI/OpenAI SDK), non-goal "not an agent framework", new "Local-first by design" section.

New category 05-Development/

• Contributing — ground rules, branch naming, Conventional Commits, one-change-per-PR, PR lifecycle, quality bar.
• Cookbooks — full offline/live recipe catalog including the new LangGraph + CrewAI recipes, with the instrumentation gotchas we hit live.
• Releasing — versioning policy, release checklist, tag-triggered publish.

Testing

• pnpm build succeeds; static /docs output contains the new sections ("Recovery Step Ratio", Development nav)
• Product untouched: make lint pass, 227 tests green

Checklist

• Exactly one logical change in this PR
• make lint passes
• uv run python -m pytest is green (227 passed)
• Docs updated if user-facing
• CHANGELOG entry — n/a (site content, not package behavior)
• Conventional title: docs(site): sync RSR/privacy/cookbook docs, add contributing guide