calendar: pull October's sanctoral calendar (pre-1955 pull, 10/12)

16 saints (14 real winners + 2 stubs). Three monastic-calendar-specific
finds this month: Ss. Placid and Companions (Oct 5, St. Benedict's own
disciple, Duplex II. classis -- absent from the base Tridentine table
entirely), St. Justina (Oct 7, reassigns what the base table gives to
St. Marcus, Pope), and St. Gall (Oct 16, founder of St. Gallen, also
absent from the base table). No octave-gap exclusions this month.

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

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

@@ -0,0 +1,8 @@
+# Verified against Divinum Officium (Monastic Tridentinum 1617), live
+# kalendar check (2025-10-14) -- winner outright, Duplex, alone. Own
+# proper collect, no unique antiphon of his own.
+id: st-callistus
+name: "St. Callistus I, Pope and Martyr"
+rank: duplex
+common: common-of-a-martyr-bishop
+propers: "st-callistus"