calendar: pull February's sanctoral calendar (pre-1955 pull, 2/12)

13 saints for February (12 real + the Vigil of St. Matthias), all
verified winning outright on a clean per-annum date — no secondary/
commemorated stubs needed this month, unlike January.

Two new scope exclusions found this month, beyond the usual octave/
temporal-continuation and fixed Lord/BVM feast ones: the generic
"Sanctae Mariae Sabbato" Saturday votive (not a real saint) and Feb 29's
leap-year redirect of the Vigil of St. Matthias (a real but not-yet-
modeled leap-day date shift).

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

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

@@ -0,0 +1,10 @@
+# Verified against Divinum Officium (Monastic Tridentinum 1617), live kalendar
+# check (2029-02-05, no Sunday collision) -- winner outright, Semiduplex. Own
+# proper antiphon (see propers/common/st-agatha-antiphon.yml) but no unique
+# collect of her own -- Common of a Virgin Martyr supplies that instead, so
+# getDayCollect resolves honestly missing for her despite propers being set.
+id: st-agatha
+name: "St. Agatha, Virgin and Martyr"
+rank: semiduplex
+common: common-of-a-virgin-martyr
+propers: "st-agatha"