chore(docs): synchronize renderer guidance

[orga-agent]

Summary

• Synchronize renderer guidance across the root README, public package metadata, and CLI/MCP/Pi/DSH host-facing descriptions.
• Position direct HTML extraction and explicit agent-browser rendering as the two selectable page-fetch backends; direct fetch remains the default.
• Make agent-facing Pi/MCP/DSH guidance explicit: direct fetch for static/SSR/pre-rendered pages; render: "agent-browser" plus waitMs for client-rendered/SPAs; no automatic fallback.
• Explain that rendering requires a host-installed agent-browser: npm install --global agent-browser, then agent-browser install; the executable must be directly runnable from PATH without a shell.

Verification

• pnpm format:check
• pnpm typecheck
• pnpm build
• pnpm test (77 tests)
• pnpm test:pack