Add CycleCalcs to Astronomy APIs

[cyclecalcs]

Adds CycleCalcs under Astronomy APIs, in alphabetical order between astrometry.net and Open Astronomy Catalog API.

A read-only astronomy API of 29 endpoints that returns interpreted answers rather than raw ephemeris: moon phase and illumination, sunrise, sunset and twilight, planet positions and a visibility board, rise and set times, eclipses, lunar nodes and libration, seasons, retrograde stations, conjunctions and angular separation, sidereal time, the equation of time, Jupiter's Galilean moons, dark-sky windows, and a one-call sky snapshot for a location and moment.

Why it may be a useful addition to this list:

• No key, no signup, no card on the free tier. curl https://www.cyclecalcs.com/v2/moon returns 200, and CORS is *, so it works client-side.
• Every response states its conventions - reference frame, epoch, time scale and refraction model - and measured residuals are published. Positions are arcminute class for the Sun, Moon and planets from 1700 to 2200.
• Machine-readable throughout: OpenAPI description, RFC 9457 problem documents, and an MCP server exposing the same engine as tools for AI clients.
• The underlying data is public domain. Computed values are CC0, and a reproducible archive of 55,909 events covering 1700-2200 is published at cyclecalcs/astronomy-data with DOI 10.5281/zenodo.21905242. The build is byte-reproducible from a pinned open-source engine.
• Free subscribable iCalendar feeds serve the same events for anyone who wants them pushed rather than pulled.

Checked against the guidelines:

• Related to astronomy
• Link is not already listed, and no open or closed PR proposes it
• Individual PR for this one suggestion
• Added in alphabetical order within Astronomy APIs
• Name, URL and description included
• No trailing whitespace