Generalize non-Sunday movable feasts into one Easter-offset resolver

The bespoke applyImmaculateHeart function (following the applyMarianSaturday/
applyChristTheKing precedent of one hand-written override function per
feast) doesn't scale: several more feasts are planned that all reduce to
"weekday N days from Easter Sunday" (Ember/Rogation days, more
Sacred-Heart-family Marian devotions, St. Joseph's pre-1955 Eastertide
feast, Lenten Friday Passion devotions), and one-off functions invite
subtle ordering bugs -- applyImmaculateHeart had to be sequenced after
applyMarianSaturday specifically or it would have been silently clobbered.

Replaced with calendar/movable-feasts.ts's generic applyMovableFeasts,
which scans calendar/temporal-feasts.ts's existing per-feast YAML records
for a new optional `easterOffset` field. Adding the next movable feast is
now a new data/calendar/temporal-feasts/<id>.yml file with `rank` and
`easterOffset` set, not a new TypeScript function. Same rank-compared,
commemorate-the-loser semantics as before, just centralized instead of
duplicated per feast.

christ-the-king, marian-saturday, and christmas-octave-sunday stay as
their own functions -- they're structurally different rules (a fixed
month-position search, a date-less fallback default, and a fixed-date-
range Sunday search, respectively), not Easter offsets, so force-fitting
them into this table wouldn't actually simplify anything.

No behavior change -- the existing Immaculate Heart of Mary test suite
passes unchanged through the new generic path.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VZSAgRi4QE4XRTqVto93zA

src/data/calendar/temporal-feasts/immaculate-heart-of-mary.yml

@@ -2,13 +2,14 @@
 # date collided outright with the Assumption's own octave-closing day,
 # which this project also deliberately keeps (see saints/assumption.yml).
 # Moved to the Saturday after the Feast of the Sacred Heart (Easter+69,
-# see calendar/index.ts's applyImmaculateHeart) -- the feast's own real
-# diocesan date from 1914 until Pius XII's 1944 fixed-date decree, and
-# also the date Paul VI's 1969 reform returned to, so it has continuity
-# on both sides of the Aug-22 interlude. Rank/name still sourced from
+# see calendar/movable-feasts.ts) -- the feast's own real diocesan date
+# from 1914 until Pius XII's 1944 fixed-date decree, and also the date
+# Paul VI's 1969 reform returned to, so it has continuity on both sides
+# of the Aug-22 interlude. Rank/name still sourced from
 # `web/www/horas/Latin/Sancti/08-22.txt`'s own [Rank] block, same as
 # before the move -- only the date assignment changed, not the office's
 # own content.
 id: immaculate-heart-of-mary
 name: "The Immaculate Heart of the Blessed Virgin Mary"
 rank: duplex-2-classis
+easterOffset: 69