Give the Vigil of Christmas (Dec 24) its own proper content

Non-Sunday Dec 24 previously just inherited Advent 4's ferial collect and
antiphons with nothing of its own. Import the Vigil's real proper content
from the reference engine (Duplex I classis): its own collect, all 5 Lauds
antiphons, the Benedictus antiphon, and Matins' Gospel (Matt 1:18-21) +
St. Jerome homily, wired via a new `vigil-of-christmas` temporal id scoped
to non-Sunday Dec 24 only. Advent IV landing on Dec 24 itself is untouched,
left as its own separate design question.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ME8QNPdEmHSbSx1r6VmDRG

src/data/propers/nocturn-readings/vigil-of-christmas.yml

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+# Matins reading for the Vigil of Christmas (Dec 24, when it's not itself
+# Advent 4's own Sunday) -- read directly from the reference engine's
+# Sancti/12-24.txt (Lectio1, Latin) and English/Sancti/12-24.txt (Lectio1,
+# English): the day's Gospel pericope (Matt 1:18-21, given in full, not a
+# bare incipit) plus St. Jerome's homily on it. Same single-nocturn Vigil
+# shape as vigil-of-st-john-the-baptist.yml -- `nocturn: 1`, matching the
+# Ember-day convention for a ferial day's one real nocturn (see
+# hours/matins.ts's own nocturnReadingIds doc comment).
+id: vigil-of-christmas
+readings:
+  - nocturn: 1
+    isGospel: true
+    citation: { la: "Matt 1:18-21", en: "Matt 1:18-21" }
+    text:
+      la: >-
+        Cum esset desponsáta Mater Jesu María Joseph, ántequam convenírent, invénta est in útero
+        habens de Spíritu Sancto. Et réliqua.
+      en: >-
+        When as his mother Mary was espoused to Joseph, before they came together, she was found
+        with child, of the Holy Ghost. And so on.
+    status: { la: verified, en: verified }
+    responsory:
+      la: |
+        R. Sanctificámini hódie, et estóte paráti: quia die crástina vidébitis
+        * Majestátem Dei in vobis.
+        V. Hódie sciétis quia véniet Dóminus, et mane vidébitis.
+        R. Majestátem Dei in vobis.
+      en: |
+        R. Sanctify yourselves today, and be ready; for on the morrow, ye shall see
+        * The majesty of God upon you.
+        V. This day ye shall know that the Lord cometh, and in the morning, then ye shall see.
+        R. The majesty of God upon you.
+  - nocturn: 1
+    isGospel: false
+    source: "Homily by St. Jerome, Priest (at Bethlehem), Book of Commentaries, on Matth. i."
+    text:
+      la: >-
+        Quare non de símplici vírgine, sed de desponsáta concípitur? Primum, ut per generatiónem
+        Joseph, orígo Maríæ monstrarétur: secúndo, ne lapidarétur a Judǽis ut adúltera: tértio, ut
+        in Ægýptum fúgiens habéret solátium. Martyr Ignátius étiam quartam áddidit causam, cur a
+        desponsáta concéptus sit: Ut partus, ínquiens, ejus celarétur diábolo, dum eum putat non de
+        vírgine, sed de uxóre generátum.
+      en: >-
+        Why was the Lord conceived of an espoused virgin rather than of a free? First, for the
+        sake of the genealogy of Mary, which we have obtained by that of Joseph. Secondly, because
+        she was thus saved from being stoned by the Jews as an adulteress. Thirdly, that Himself
+        and His mother might have a guardian on their journey into Egypt. To these, Ignatius, the
+        martyr of Antioch, has added a fourth reason namely, that the birth might take place
+        unknown to the devil, who would naturally suppose that Mary had conceived by Joseph.
+    status: { la: verified, en: verified }

src/data/propers/temporal/vigil-of-christmas-benedictus-antiphon.yml

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+# Verified against Divinum Officium (Monastic Tridentinum 1617), Lauds
+# live query, 2026-12-24 (a plain Thursday, non-Sunday Vigil of
+# Christmas). The static reference file (Sancti/12-24.txt) has no
+# explicit `[Ant Benedictus]` tag for this date -- turns out the live
+# engine reuses the same text tagged `[Ant 2]` there (labeled "Antiphona
+# ex Proprio Sanctorum" in the live render), already imported separately
+# for Matins' own Nocturn 2 -- see nocturn-readings/vigil-of-christmas.yml.
+# Same text, two real uses, not a coincidence to collapse into one file:
+# these are two distinct ResolvedPart slots.
+id: vigil-of-christmas-benedictus-antiphon
+text:
+  la: "Oriétur * sicut sol Salvátor mundi: et descéndet in úterum Vírginis, sicut imber super gramen, allelúja."
+  en: "The Saviour of the world * shall rise like the sun, and come down into the womb of the Virgin as the showers upon the grass, alleluia."
+status:
+  la: verified
+  en: verified

src/data/propers/temporal/vigil-of-christmas-collect.yml

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+# Read directly from the reference engine's own Sancti/12-24.txt (Latin)
+# and English/Sancti/12-24.txt -- the Vigil of Christmas's own proper
+# Oratio (`In Vigilia Nativitatis Domini`, Duplex I classis), used on Dec
+# 24 regardless of rank contest (see calendar/temporal-id.ts's own
+# `vigil-of-christmas` case, currently scoped to a non-Sunday Dec 24 only).
+id: vigil-of-christmas-collect
+text:
+  la: |
+    Orémus.
+    Deus, qui nos redemptiónis nostræ ánnua exspectatióne lætíficas: præsta; ut Unigénitum tuum, quem Redemptórem læti suscípimus, veniéntem quoque Júdicem secúri videámus, Dóminum nostrum Jesum Christum Fílium tuum:
+    Qui tecum vivit et regnat in unitáte Spíritus Sancti, Deus, per ómnia sǽcula sæculórum.
+    R. Amen.
+  en: |
+    Let us pray.
+    O God, thou Who gladden us year after year with the expectation of our redemption, grant that we, who now welcome with joy thy only-begotten Son as our Redeemer, may also gaze upon Him without fear when He comes as our judge, our Lord Jesus Christ, thy Son:
+    Who liveth and reigneth with thee, in the unity of the Holy Spirit, God, world without end.
+    R. Amen.
+status:
+  la: verified
+  en: verified