calendar: pull September's sanctoral calendar (pre-1955 pull, 9/12)

14 saints (12 real winners + 2 stubs), plus a propers-slug update for the
pre-existing Nativity of the BVM entry. Two monastic-calendar-specific
finds: St. Nicholas of Tolentino (Sep 10) overrides what the base
Tridentine table treats as a plain Nativity-octave continuation, and St.
Januarius (Sep 19) is a monastic-only addition absent from the base table
entirely. Also flags (not yet acted on) that the pre-existing Sep 29 St.
Michael mapping doesn't appear to hold in this pull's actual target
track -- see the sanctoral-calendar.yml comment for detail.

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

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

@@ -0,0 +1,11 @@
+# A monastic-calendar-specific addition: not present in the base Tridentine
+# table (1570.txt), added by the monastic-specific delta table
+# (M1617.txt). Verified live (Monastic Tridentinum 1617, 2025-09-19) --
+# winner outright, Semiduplex, alone (the only other candidate that day is
+# a September Ember Friday feria, not another saint). No unique collect:
+# the raw file at this MM-DD slot (Sancti/09-19.txt) is empty.
+id: st-januarius
+name: "St. Januarius, Bishop, and Companions, Martyrs"
+rank: semiduplex
+common: common-of-a-martyr-bishop
+propers: null