Jan 1 previously fell through to generic Christmastide-feria content with
no identity of its own, despite being Christmas's own Octave Day. Adds a
`fixed-date` anchor kind to calendar/movable-feasts.ts's MovableAnchor
(the existing easter/nth-sunday kinds can't express "always Jan 1"),
plus the feast's collect, Magnificat/Benedictus antiphons, full Lauds
psalmody, capitulum, versicle, and two Matins nocturn readings (Leo the
Great, Ambrose), sourced from Sancti/01-01.txt.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014axryJBrRswYh2niA7WCUc
