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/assumption-collect.yml

@@ -0,0 +1,17 @@
+# Verified against Divinum Officium (Monastic Tridentinum 1617) — read
+# directly from the reference engine's own real-date output (2025-08-15).
+id: assumption-collect
+text:
+  la: |
+    Orémus.
+    Famulórum tuórum, quǽsumus, Dómine, delíctis ignósce: ut qui tibi placére de áctibus nostris non valémus: Genitrícis Fílii tui Dómini nostri intercessióne salvémur:
+    Qui tecum vivit et regnat in unitáte Spíritus Sancti, Deus, per ómnia sǽcula sæculórum.
+    ℟. Amen.
+  en: |
+    Let us pray.
+    O Lord, we beseech thee, forgive the transgressions of thy servants, and, forasmuch as by our own deeds we cannot please thee, may we find safety through the prayers of the Mother of thy Son and our Lord.
+    Who with thee liveth and reigneth, in the unity of the Holy Spirit, God, world without end.
+    ℟. Amen.
+status:
+  la: verified
+  en: verified