propers: add August's collect and antiphon text

11 collects, 4 antiphons -- including backfilling the three pre-existing
August entries (Lawrence, Assumption, Augustine) now that the pulling
methodology exists. Also updates three pre-existing tests whose dates
collided with this month's new real content: the vigil-of-St.-Lawrence
backward-transfer case now runs into a real feast at its landing day
instead of an empty one (confirmed correct against the live reference
engine, including the surviving commemoration on the impeded Sunday
itself), and two other tests moved off Aug 9/10 to dates unaffected by
the new data.

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

src/data/propers/common/finding-of-st-stephen-collect.yml

@@ -0,0 +1,19 @@
+# Verified against Divinum Officium (Monastic Tridentinum 1617) — read
+# directly from the reference engine's own real-date output (2026-08-03),
+# which auto-expands the raw file's cross-reference to St. Stephen's Dec
+# 26 collect with "natalícia" substituted for "Inventiónem".
+id: finding-of-st-stephen-collect
+text:
+  la: |
+    Orémus.
+    Da nobis, quǽsumus, Dómine, imitári quod cólimus: ut discámus et inimícos dilígere; quia ejus Inventiónem celebrámus, qui novit étiam pro persecutóribus exoráre 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.
+    Grant us, we beseech thee, O Lord, so to imitate what we revere, that we may learn to love even our enemies; for we celebrate the Finding of the holy body of him who knew how to pray for his very persecutors to our Lord Jesus Christ:
+    Who with thee liveth and reigneth, in the unity of the Holy Spirit, God, world without end.
+    ℟. Amen.
+status:
+  la: verified
+  en: verified