feat: add PS-Wiki remote MCP service

[leocuisine]

Summary

• add a stateless, read-only remote MCP Worker backed by the existing REST API
• expose the five PS-Wiki MCP tools with bounded validation, timeouts, response limits, safe errors, and read-only annotations
• publish canonical service hosts at api.ps-wiki.ning.guru and mcp.ps-wiki.ning.guru/mcp
• add deterministic Worker/Python tests, deployment workflows, and updated documentation

Deployment verification

• Cloudflare Workers deployed and custom domains live
• REST probes: /, /v1/terms, /v1/tags, and /openapi.json returned 200
• MCP initialize and tools/list verified; live REST-backed tool calls verified during deployment
• npm ci and npm run check (7 Worker tests)
• Python MCP tests (5 passed), Ruff, byte-compilation, Prettier, and git diff --check

Notes

The old api.ning.guru and mcp.ning.guru bindings were intentionally removed per the approved direct hostname cutover. No unrelated DNS or nameserver changes were made.