Generalize movable-feast anchors beyond Easter offsets, migrate Christ the King

Extends TemporalFeastRecord's date anchor from a single easterOffset
number into a MovableAnchor union: 'easter' (unchanged), plus
'nth-sunday-of-month' (nth: -1 for "last") and 'nth-sunday-of-advent' --
both new anchor kinds resolve to "Nth Sunday counting from an anchor
date," just with a different anchor (first-of-month vs. Advent's own
start, which is itself always a Sunday). Adds calendar/temporal.ts's
sundayOnOrAfter to support the month case.

Migrates christ-the-king.yml onto the new nth-sunday-of-month anchor
(month: 10, nth: -1) with a new `unconditional: true` flag replacing its
old always-wins-no-rank-check bespoke function -- retiring
applyChristTheKing and its lastSundayOfOctober helper from
calendar/index.ts entirely. Down to two bespoke override functions left
(marian-saturday's date-less fallback, christmas-octave-sunday's
fixed-date-range Sunday search), both structurally different from the
Nth-Sunday-from-anchor shape this table now covers.

No behavior change -- the full existing Christ the King 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/christ-the-king.yml

@@ -3,7 +3,14 @@
 # instead (the Monastic-lineage version of the era that actually carries
 # it), confirmed live: last Sunday of October, Duplex I. classis,
 # commemorating whichever Sunday after Pentecost it would otherwise be.
-# See calendar/index.ts's applyChristTheKing for the occurrence rule.
+# Per direct instruction, `unconditional: true` -- always wins the last
+# Sunday of October full stop, no rank check at all, unlike every other
+# movable feast. See calendar/movable-feasts.ts for the occurrence rule.
 id: christ-the-king
 name: "Christ the King"
 rank: duplex-1-classis
+anchor:
+  kind: nth-sunday-of-month
+  month: 10
+  nth: -1
+unconditional: true

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

@@ -12,4 +12,6 @@
 id: immaculate-heart-of-mary
 name: "The Immaculate Heart of the Blessed Virgin Mary"
 rank: duplex-2-classis
-easterOffset: 69
+anchor:
+  kind: easter
+  offset: 69