Restructure documentation content

[cdebled]

New structure

• Introduction
• Quickstart — merged from 4 separate pages into one
• Run locally — renamed from Open Source
  • Installation — split from a single page into sub-pages
    • One-liner
    • Docker
    • Package managers — new page, content from upstream installation.mdx
    • Nightly builds
    • System requirements — moved from Run locally root
    • Build from sources — moved from Guides
  • Commands — new sub-section, content split out of usage.mdx
    • Fetch (+ options)
    • CDP server (+ options)
  • Configure a proxy — moved from Guides
• Run on Lightpanda Cloud — renamed from Cloud Offer
  • Getting started
• Usage — new top-level section
  • CDP — content from cloud-offer/tools/cdp.mdx, split into one page per client, with Local/Cloud tabs
    • Puppeteer
    • Playwright
    • Chromedp
  • MCP — content from cloud-offer/tools/mcp.mdx (Cloud tab) and guides/mcp-server.mdx (Local tab, with full JSON-RPC examples, resources, supergateway, known behaviors)
  • HTTP API — moved from cloud-offer/tools/api.mdx
• Guides — moved from under Run locally to a top-level section
  • Retrieve an HTML webpage — new
  • Get a markdown version — moved from Run locally guides
  • Interact with a webpage — new
  • Use Stagehand — moved from Run locally guides
  • Use Hermes Agent — new, from upstream

Test plan

• Verify sidebar navigation matches the new structure
• Check all internal links resolve correctly
• Verify Local/Cloud tabs work on Usage/CDP and Usage/MCP pages
• Confirm Quickstart renders correctly as a single page

[krichprollsch]

closed in favor of #67