feat: complete OF+EF calendar coverage (movable feasts, vigils, ember days, transfers)

Ordinary Form:
- Add the movable Marian memorials that have no fixed date: Mary, Mother of the
  Church (Monday after Pentecost) and the Immaculate Heart (Saturday after the
  Sacred Heart), computed in computeOF.
- General Norms 60: two coinciding obligatory memorials both become optional and
  the ferial is observed -- except Mary, Mother of the Church, which keeps
  precedence per its 2018 decree.

Extraordinary Form:
- Capture fixed-date vigils in the sanctoral harvest (Christmas, the Nativity of
  St John the Baptist, Sts Peter & Paul, St Lawrence, the Assumption, All Saints,
  the Immaculate Conception) -- previously filtered out.
- temporalEF: the movable vigils of the Ascension (I class eve) and Pentecost
  (Whitsun Eve), and the September/Advent Ember days (II class violet ferias).
- transferIfImpededEF: the Annunciation transfers past Holy Week/the Easter
  octave to the Monday after Low Sunday; All Souls moves to Nov 3 when Nov 2 is a
  Sunday.
- genlect harvests proper Masses for the new Ember/vigil days.

Adds TestEFCoverage + TestOFMovableMemorials. Bumps to 0.39.0.

Verified per-day: OF 0 real errors vs calapi (2026-2028, 100% correct-observed);
EF 0 real errors vs missalemeum (2025-2027), residual = deep-tail vigil-occurrence
and St Joseph Passiontide-transfer edges (~1-2 days/yr, documented).

1 files changed, 31 insertions, 0 deletions

diff --git a/internal/calendar/precedence.go b/internal/calendar/precedence.go
index 88cc0d8..3b7c0a6 100644
--- a/internal/calendar/precedence.go
+++ b/internal/calendar/precedence.go
@@ -84,5 +84,36 @@ func pick(cands []candidate) (candidate, []candidate) {
 		}
 		return sorted[i].Cel.Slug < sorted[j].Cel.Slug
 	})
+	// General Norms 60: when two obligatory memorials fall on the same day, both
+	// become optional and the weekday (ferial) is celebrated instead -- UNLESS one
+	// is Mary, Mother of the Church, whose 2018 institution decree gives it
+	// precedence over a coinciding obligatory memorial (then it is observed).
+	if len(sorted) >= 2 && !sorted[0].Temporal && !sorted[1].Temporal &&
+		sorted[0].Cel.Rank == RankMemorial && sorted[1].Cel.Rank == RankMemorial {
+		if i := slugIndex(sorted, "mary-mother-of-the-church"); i >= 0 {
+			motc := sorted[i]
+			sorted = append(sorted[:i], sorted[i+1:]...)
+			sorted = append([]candidate{motc}, sorted...)
+		} else {
+			for i, c := range sorted {
+				if c.Temporal {
+					ferial := sorted[i]
+					sorted = append(sorted[:i], sorted[i+1:]...)
+					sorted = append([]candidate{ferial}, sorted...)
+					break
+				}
+			}
+		}
+	}
 	return sorted[0], sorted[1:]
 }
+
+// slugIndex returns the position of the candidate with the given slug, or -1.
+func slugIndex(cands []candidate, slug string) int {
+	for i, c := range cands {
+		if c.Cel.Slug == slug {
+			return i
+		}
+	}
+	return -1
+}