propers: add May's collect and antiphon text

Real collect text for all 13 May saints that have one, plus a real
antiphon for the 3 that have one of their own (Ss. Philip and James, St.
John Before the Latin Gate, the Apparition of St. Michael) — same
extraction method as prior months. Two saints (St. Peter Celestine, St.
Urban I) have an [Ant 1] in the source that turned out to just be a
cross-reference to the generic Common template, not real unique text, so
no antiphon file was authored for them.

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

src/data/propers/common/st-peter-celestine-collect.yml

@@ -0,0 +1,18 @@
+# Verified against Divinum Officium (Monastic Tridentinum 1617) — read
+# directly from the reference engine's own real-date output (2038-05-19).
+# Same convention as data/propers/temporal/*-collect.yml.
+id: st-peter-celestine-collect
+text:
+  la: |
+    Orémus.
+    Deus, qui beátum Petrum Cælestínum ad summi pontificátus ápicem sublimásti, quique illum humilitáti postpónere docuísti: concéde propítius; ut ejus exémplo cuncta mundi despícere, et ad promíssa humílibus prǽmia perveníre felíciter mereámur.
+    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 raised blessed Peter Celestine to the lofty dignity of Supreme Pontiff and taught him to prefer self-abasement instead; mercifully grant that by his example we may look upon all worldly things as naught, and may be worthy to reap in joy the rewards promised to the humble.
+    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