feat: MCP server template, manual, and example servers ...

Add canonical scaffolding for MCP server development:

- manuals/write_mcp_server.md: full guide covering structure, validation,
  smoke-testing, registration, and troubleshooting
- mcp-servers/_template/: annotated starter with annotated mcp_server.py
  and pyproject.toml for FastMCP + pydantic
- mcp-servers/project_health/: example server with 3 tools
  (get_project_summary, find_duplicate_files, get_project_dependencies)
- mcp-servers/time_toolkit/: example server with 4 tools
  (get_current_time, convert_timezone, add_time, format_datetime)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>