[cemheren]

Adds a new extension to the directory: moon: — a live lunar-phase widget published at Deskworks/quicksheet-moon-ext.

Why

A genuinely novel vertical not yet covered by any of the existing extensions: an ambient moon-phase cell for the desktop-wallpaper grid. Targets the r/unixporn/ricer persona who wants a clean, low-noise sky widget that needs zero setup.

What makes it solid

• Fully offline & deterministic — phase computed locally from the synodic month (anchored to a known new moon). No network, no API key, no rate limits, never flickers offline. Ideal for a cell that lives on a wallpaper 24/7.
• Verified against the Apollo 11 date (1969-07-20 → Waxing Crescent, ~5 days after the July 1969 new moon).
• Zero NuGet deps, .NET 9, builds clean (0 warnings / 0 errors).

Usage

moon:                  → 🌓 First Quarter  ·  37% lit  ·  age 6.2d
moon: 2026-12-25       → 🌕 Full Moon  ·  99% lit  ·  age 15.7d
moon: next full        → 🌕 next full moon: 2026-06-29  (8d away)
moon: next new         → 🌑 next new moon: 2026-07-14  (23d away)

Changes in this PR (docs only on the main repo)

• README extension table: new moon: row.
• docs/extensions.md: full-directory entry.
• docs/tour.md: extension list entry.
• Scaffold source included under .claude/skills/grow-quicksheet/drafts/extensions/quicksheet-moon-ext/ (reference copy; the live repo is already pushed).

Extension repo is already created and pushed; this PR only adds the cross-links and the reference scaffold. No main-project code changed.