calendar: pull May's sanctoral calendar (pre-1955 pull, 5/12)

18 saints for May (16 real + 2 stubs). Both stubs this month are
genuinely unwinnable in the real historical calendar in any year (their
competing observances are fixed-date, not movable) — flagged explicitly
in their own files as distinct from the usual "just an artifact of the
year checked" caveat.

A second, distinct feast of St. Michael (his Apparition, May 8) is kept
as its own record separate from st-michael.yml's Sept 29 dedication
feast, same precedent as the two Chair-of-Peter feasts.

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

src/data/calendar/sanctoral-calendar.yml

@@ -83,6 +83,30 @@ days:
   "04-28": [st-vitalis]
   "04-29": [st-robert, st-catherine-of-siena]
   "04-30": [st-peter-martyr]
+  # May — 5/12 of the pre-1955 pull. Same exclusions as before: fixed
+  # feasts of the Lord (Finding of the Holy Cross May 3), and movable
+  # ones (Ascension, Trinity Sunday, Corpus Christi — all skipped as
+  # primary, since they're temporal, not sanctoral). Two stubs this month
+  # (Ss. Alexander/Eventius/Theodulus/Juvenal, St. Pudentiana) are
+  # genuinely un-winnable in any year, not just an artifact of which year
+  # was checked — see their own files.
+  "05-01": [ss-philip-and-james]
+  "05-02": [st-athanasius]
+  "05-03": [ss-alexander-eventius-theodulus-and-juvenal]
+  "05-04": [st-monica]
+  "05-06": [st-john-before-the-latin-gate]
+  "05-07": [st-stanislaus]
+  "05-08": [apparition-of-st-michael]
+  "05-09": [st-gregory-nazianzen]
+  "05-12": [ss-nereus-achilleus-domitilla-and-pancras]
+  "05-14": [st-boniface]
+  "05-16": [st-ubald]
+  "05-19": [st-peter-celestine, st-pudentiana]
+  "05-22": [st-romanus-abbot]
+  "05-25": [st-urban-i]
+  "05-26": [st-eleutherius]
+  "05-27": [st-john-i]
+  "05-30": [st-felix-i]
   "08-09": [vigil-of-st-lawrence]
   "08-10": [st-lawrence]
   "08-15": [assumption]