Extract shared Commons for Prime/Terce/Sext/None minor-hour content

A systematic diff across all 29 duplex-majus+ saints' P/T/S/N files found
real shared-Common groups beyond the pairs noticed in passing while
authoring them. Extracted into shared data/propers/common/{hour}-antiphon-
common-of-*.yml / {hour}-capitulum-common-of-*.yml files and wired via a
new SaintRecord.minorHoursCommon field, with resolveMinorHourAntiphon/
resolveMinorHourChapter falling back to it when a saint has no proper file
of their own. Deliberately a separate field from the existing (previously
unused) `common` field: the minor hours don't always draw from the same
Common category as the saint's overall classification -- both Chair of
St. Peter feasts are `common: common-of-an-apostle` by rank, but their
P/T/S/N content is Common of a Confessor Bishop (Peter considered as
bishop of that see).

Four groups extracted (87 duplicate files collapsed to 21 shared ones),
each confirmed byte-identical via diff first: common-of-apostles (8
saints, all 4 hours), common-of-a-confessor-bishop (Chair of Peter pair
share antiphons+chapters, Martin of Tours shares only chapters), common-
of-the-bvm (Nativity BVM + Immaculate Conception's Sext/None/Terce
chapters -- the Assumption's own stay proper, different reading + proper
versicles), and common-of-st-peter (St. Peter ad Vincula + Ss. Peter and
Paul, not a real Common category, just genuinely identical Petrine
content).

Deliberately left un-extracted: St. Mark, St. John Before the Latin Gate,
and Ss. Philip and James share identical text that live-checking shows is
Paschaltide-seasonal (all three landed within the Easter octave weeks on
their queried dates, despite disagreeing `common` classifications) rather
than a fixed per-saint-category Common -- folding it into the same
mechanism would misrepresent season-contingent content as timeless. Left
as individually-authored files; flagged in TODO.md as needing a real
Paschaltide-awareness mechanism this app doesn't have yet for any hour.

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

src/data/calendar/saints/immaculate-conception.yml

@@ -7,6 +7,7 @@ name: "The Immaculate Conception of the Blessed Virgin Mary"
 rank: duplex-1-classis
 common: common-of-the-bvm
 propers: "immaculate-conception"
+minorHoursCommon: common-of-the-bvm
 # Has a real octave (Dec 8-15) -- see calendar/types.ts's OctaveConfig.
 octave:
   enabled: true