Add the Circumcision of Our Lord (Jan 1) as a proper temporal feast

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

src/data/propers/common/lauds-versicle-circumcision.yml

@@ -0,0 +1,9 @@
+# See vespers-versicle-circumcision.yml's own note — the source's own
+# [Versum 2] is "@:Versum 1", the identical text reused at Lauds.
+id: lauds-versicle-circumcision
+text:
+  la: "V. Verbum caro factum est, allelúja.\nR. Et habitávit in nobis, allelúja."
+  en: "V. The Word was made flesh, alleluia.\nR. And dwelt among us, alleluia."
+status:
+  la: verified
+  en: verified