Author real proper Matins/Vespers content for the Nativity of St. John the Baptist

nativity-of-st-john-the-baptist.yml's `common` field (common-of-an-apostle)
was the same mistaken placeholder as the Beheading's, but this feast
needed a different fix: the reference engine assigns it no Commune at
all -- every [Rule] line in Sancti/06-24.txt and SanctiM/06-24.txt points
to proper text, never a Commune category -- so there's no better-fitting
id to swap in either.

Authored the real proper content that was still falling through to the
apostle Common, live-verified against the local Divinum Officium CGI
instance (Monastic Tridentinum 1617):

- Matins invitatory antiphon ("Regem Præcursóris Dóminum")
- Matins hymn ("Antra desérti téneris," with the Monastic doxology
  substitution already used by this feast's own Lauds/Vespers hymns)
- Full Matins Nocturn 1-3 psalmody + nocturn versicles (Nocturn 1/2 reuse
  St. Lawrence's own shared psalm-number pool per "Psalmi Dominica";
  Nocturn 3 reuses St. Lawrence's own canticle scripture files verbatim,
  since the citations are identical)
- Vespers psalmody (only 4 psalm slots at this Monastic rank, not 5 as a
  naive reading of the raw Ant Vespera list would suggest)
- Nocturn 2/3 responsories on the existing nocturn-readings file

`common: common-of-an-apostle` is left in place as a fully inert
placeholder (a non-optional field with no better id available) with an
updated comment explaining why.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WvnBMq7HGfXRyMsVLu2v4D

src/data/propers/common/matins-hymn-nativity-of-st-john-the-baptist.yml

@@ -0,0 +1,65 @@
+# Verified against Divinum Officium — Sancti/06-24.txt's own [Hymnus
+# Matutinum], with the Monastic doxology substitution from [HymnusM
+# Matutinum] applied (s/posses/saltem/ s/Crímine linguæ/Flámine posses/
+# s/durum/hirtum/ s/Sit decus/Glória/ s/semper/alme/ s/virtus/semper/
+# s/Témporis ævo/Témpore sæcli/ — same substitution set already applied
+# for vespers-hymn-nativity-of-st-john-the-baptist.yml, whose doxology
+# it exactly matches). English is the reference's own translation,
+# already in the Monastic doxology form.
+id: matins-hymn-nativity-of-st-john-the-baptist
+text:
+  la: |
+    Antra desérti téneris sub annis,
+    Cívium turmas fúgiens, petísti,
+    Ne levi saltem maculáre vitam
+    Flámine posses.
+
+    Prǽbuit hirtum tégumen camélus
+    Artubus sacris, stróphium bidéntes;
+    Cui latex haustum, sociáta pastum
+    Mella locústis.
+
+    Céteri tantum cecinére Vatum
+    Corde præságo jubar affutúrum;
+    Tu quidem mundi scelus auferéntem
+    Indice prodis.
+
+    Non fuit vasti spátium per orbis
+    Sánctior quisquam génitus Joánne,
+    Qui nefas sæcli méruit lavántem
+    Tíngere lymphis.
+
+    Glória Patri, genitǽque Proli,
+    Et tibi, compar utriúsque semper,
+    Spíritus alme, Deus unus omni
+    Témpore sæcli.
+    Amen.
+  en: |
+    Thou, in thy childhood, to the desert caverns
+    Fleddest for refuge from the cities' turmoil,
+    Where the world's slander might not dim thy lustre,
+    Lonely abiding.
+
+    Camel's hair raiment clothed thy saintly members;
+    Leathern the girdle which thy loins encircled;
+    Locusts and honey, with the fountain-water,
+    Daily sustained thee.
+
+    Oft in past ages, seers with hearts expectant
+    Sang the far-distant advent of the day-star;
+    thine was the glory, as the world's Redeemer
+    First to proclaim him.
+
+    Far as the wide world reacheth, born of woman,
+    Holier was there none than John the Baptist;
+    Meetly in water laving him who cleanseth
+    Man from pollution.
+
+    Praise to the Father, to the Son begotten,
+    And to the Spirit, equal power possessing,
+    One God whose glory, through the lapse of ages,
+    Ever resoundeth.
+    Amen.
+status:
+  la: verified
+  en: verified