propers: add June's collect and antiphon text

Real collect text for all 16 June saints that have one, plus a real
antiphon for 4 of them and a fifth (Ss. Peter and Paul) that deliberately
reuses the Chair-of-Peter-at-Antioch antiphon text, matching the source's
own cross-reference — same extraction method as prior months.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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

@@ -0,0 +1,18 @@
+# Verified against Divinum Officium (Monastic Tridentinum 1617) — read
+# directly from the reference engine's own real-date output (2035-06-24).
+# Same convention as data/propers/temporal/*-collect.yml.
+id: nativity-of-st-john-the-baptist-collect
+text:
+  la: |
+    Orémus.
+    Deus, qui præséntem diem honorábilem nobis in beáti Joánnis nativitáte fecísti: da pópulis tuis spirituálium grátiam gaudiórum; et ómnium fidélium mentes dírige in viam salútis ætérnæ.
+    Per Dóminum nostrum Jesum Christum, Fílium tuum: qui tecum vivit et regnat in unitáte Spíritus Sancti, Deus, per ómnia sǽcula sæculórum.
+    ℟. Amen.
+  en: |
+    Let us pray.
+    O God, Who hast made this day to be honourable in our eyes because of the Birth of the blessed John, graciously quicken thy people with spiritual joy, and order the minds of all the faithful in the way of everlasting salvation.
+    Through Jesus Christ, thy Son our Lord, Who liveth and reigneth with thee, in the unity of the Holy Ghost, God, world without end.
+    ℟. Amen.
+status:
+  la: verified
+  en: verified