calendar: pull August's sanctoral calendar (pre-1955 pull, 8/12)

18 saints (14 real winners + 4 stubs), plus propers-slug updates for the
4 pre-existing August entries. Notable this month: several dates have a
real named secondary saint permanently subordinate to an unmodeled fixed
octave (Lawrence's own, the Assumption's) or the fixed Transfiguration --
excluded entirely rather than guessed at, since this app can't yet
represent the actual blocking primary (a known, deferred octave gap).
Most notable casualty: St. Clare (Aug 12).

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

src/data/calendar/saints/st-bernard.yml

@@ -0,0 +1,10 @@
+# Verified against Divinum Officium (Monastic Tridentinum 1617), live
+# kalendar check (2025-08-20) -- winner outright, Duplex, over the sixth
+# day of the Assumption's octave (a fixed BVM feast, out of scope, see
+# the sanctoral-calendar.yml comment on this month's octave exclusions).
+# Own proper collect, no unique antiphon of his own.
+id: st-bernard
+name: "St. Bernard, Abbot and Doctor of the Church"
+rank: duplex
+common: common-of-an-abbot
+propers: "st-bernard"