docs: add comprehensive WebSocket server guide

[MikiEEE]

Summary

• move the public documentation previously included in PR feat: add bounded WebSocket server support #7 into a dedicated follow-up
• make README the concise landing page for the reconciled managed-runtime, regex-routing, and WebSocket API
• add the 13-page guide covering setup, routing, requests/responses, lifecycle, configuration, adapters, observability, kernels, WebSockets, API reference, roadmap, and development
• compile every Python fence and validate every relative Markdown link in tests

Stack

This PR intentionally targets feat/websocket-server so its review diff is documentation-only. Merge PR #7 first, then retarget this PR to develop if GitHub does not update the base automatically.

Boundary

The diff contains only README.md, guide/*.md, and tests/test_documentation.py. WebSocket implementation, configuration, demos, examples, and protocol tests remain in PR #7.

Validation

• complete inherited suite plus docs: 153 passed
• documentation inventory, relative links, heading fragments, and Python code fences pass
• compileall and git diff --check pass
• documentation accuracy remediation fixed direct-await and stale routing/error wording after the branch reconciliation