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, 75 insertions, 0 deletions

diff --git a/internal/calendar/coverage_test.go b/internal/calendar/coverage_test.go
new file mode 100644
index 0000000..e6555b9
--- /dev/null
+++ b/internal/calendar/coverage_test.go
@@ -0,0 +1,75 @@
+package calendar_test
+
+import (
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/lukaszkasprzak/lectio/internal/caldata"
+	"github.com/lukaszkasprzak/lectio/internal/calendar"
+)
+
+func day(y int, m time.Month, d int) time.Time {
+	return time.Date(y, m, d, 0, 0, 0, 0, time.UTC)
+}
+
+// TestEFCoverage checks the EF special days added for full coverage: the movable
+// vigils, the September/Advent Ember days, and the transfer of an impeded feast.
+// (2027: Easter is March 28.)
+func TestEFCoverage(t *testing.T) {
+	sel := calendar.DefaultSelection()
+	sel.Form = "old"
+	layers := []calendar.Layer{caldata.Tridentine()}
+
+	cases := []struct {
+		date time.Time
+		slug string
+		rank calendar.Rank
+	}{
+		{day(2027, time.September, 22), "ef-september-ember-wed", calendar.RankClass2},
+		{day(2027, time.December, 15), "ef-advent-ember-wed", calendar.RankClass2},
+		{day(2027, time.May, 5), "ef-ascension-vigil", calendar.RankClass2},
+		{day(2027, time.May, 15), "ef-pentecost-vigil", calendar.RankClass1},
+		{day(2027, time.June, 23), "vigil-of-the-nativity-of-st-john-the-baptist", calendar.RankClass2},
+		// Annunciation (Mar 25) is in Holy Week in 2027, so it is transferred to
+		// the Monday after Low Sunday (Apr 5); Mar 25 itself keeps the Triduum.
+		{day(2027, time.April, 5), "annunciation-of-the-blessed-virgin-mary", calendar.RankClass1},
+	}
+	for _, c := range cases {
+		got := calendar.Compute(c.date, sel, layers)
+		if got.Observed.Slug != c.slug || got.Observed.Rank != c.rank {
+			t.Errorf("%s: observed %q/%v, want %q/%v", c.date.Format("2006-01-02"),
+				got.Observed.Slug, got.Observed.Rank, c.slug, c.rank)
+		}
+	}
+	// The Annunciation must NOT also appear on its impeded fixed date.
+	if got := calendar.Compute(day(2027, time.March, 25), sel, layers); strings.Contains(got.Observed.Slug, "annunciation") {
+		t.Errorf("2027-03-25 (Holy Thursday) wrongly observes %q", got.Observed.Slug)
+	}
+	// All Souls: Nov 2 2025 is a Sunday, so it is transferred to Nov 3.
+	if got := calendar.Compute(day(2025, time.November, 3), sel, layers); got.Observed.Slug != "commemoration-of-all-souls" {
+		t.Errorf("2025-11-03: observed %q, want the transferred All Souls", got.Observed.Slug)
+	}
+}
+
+// TestOFMovableMemorials checks Mary, Mother of the Church, the Immaculate Heart,
+// and the two-obligatory-memorials rule.
+func TestOFMovableMemorials(t *testing.T) {
+	sel := calendar.DefaultSelection() // Ordinary Form
+	layers := []calendar.Layer{caldata.Universal()}
+
+	// Mary, Mother of the Church: Monday after Pentecost (2027: May 17).
+	if got := calendar.Compute(day(2027, time.May, 17), sel, layers); got.Observed.Slug != "mary-mother-of-the-church" {
+		t.Errorf("2027-05-17: observed %q, want mary-mother-of-the-church", got.Observed.Slug)
+	}
+	// Two obligatory memorials coincide (St Anthony of Padua + the Immaculate
+	// Heart, 2026-06-13): both become optional and the ferial is observed.
+	if got := calendar.Compute(day(2026, time.June, 13), sel, layers); got.Observed.Rank != calendar.RankFerial {
+		t.Errorf("2026-06-13: observed %q/%v, want the ferial", got.Observed.Slug, got.Observed.Rank)
+	}
+	// But Mary, Mother of the Church keeps precedence over a coinciding memorial
+	// (2028-06-05, with St Boniface).
+	if got := calendar.Compute(day(2028, time.June, 5), sel, layers); got.Observed.Slug != "mary-mother-of-the-church" {
+		t.Errorf("2028-06-05: observed %q, want mary-mother-of-the-church", got.Observed.Slug)
+	}
+}