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/st-leo-ii-collect.yml

@@ -0,0 +1,18 @@
+# Verified against Divinum Officium (Monastic Tridentinum 1617) — read
+# directly from the reference engine's own real-date output (2035-06-28).
+# Same convention as data/propers/temporal/*-collect.yml.
+id: st-leo-ii-collect
+text:
+  la: |
+    Orémus.
+    Deus, qui beátum Leónem Pontíficem sanctórum tuórum méritis coæquásti: concéde propítius; ut, qui commemoratiónis ejus festa percólimus, vitæ quoque imitémur exémpla.
+    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 didst make the blessed Pope Leo to work deeds worthy of thy Saints, mercifully grant that we who do keep glad holiday in his memory, may steadfastly follow after the example of his life.
+    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