Merge branch 'polish-ui-and-calendar': the gomobile facade and the EF calendar fixes

Two bodies of work that shared a branch.

The gomobile facade (2026-08-03..05): mobile.PartLabels, Days, and the
observed rank on DayInfo, so dlectio stops hardcoding part IDs and rank
strings; the 1962 part labels become i18n data; the documented gomobile
bind command is corrected so it reproduces the shipped .aar.

The EF calendar fixes (2026-08-12): seven defects found by differencing
this engine against colitur, a second 1962 implementation built from the
Missal's General Rubrics rather than from this codebase. RG 96 transfers
were not skipping II-class days; a II-class privileged feria was not
yielding to a feast; Sunday ranks, the two Rose Sundays and Holy Thursday's
colour were wrong; and scripts/gen-sanctoral-ef inferred ranks, deduped
and tagged classes wrongly, which put 15 III-class feasts into the shipped
tridentine-calendar.ini as bare commemorations and dropped four entries
outright.

Holy Thursday was violet in both engines, which is how a shared lineage
hides a defect: this project's ini is generated from missalemeum and
colitur's data was bootstrapped from here, so an error inherited by both
is invisible to a differential. It took the Missal itself to see it.

The EF oracle test now asserts rank and colour, not season alone. One
known gap is recorded in the source rather than fixed, as out of scope:
RG 95 chained transfers (calendar.go).

1 files changed, 9 insertions, 0 deletions

diff --git a/internal/liturgy/section.go b/internal/liturgy/section.go
index dcca7b5..baf2b9d 100644
--- a/internal/liturgy/section.go
+++ b/internal/liturgy/section.go
@@ -33,4 +33,13 @@ type DayInfo struct {
 	// Colour is the normalized liturgical colour: "white", "green",
 	// "violet", "red", "rose", or "" when unknown/unmapped.
 	Colour string
+	// Rank is the normalized liturgical rank of the observed celebration:
+	// the Ordinary Form's "ferial", "optional", "memorial", "feast",
+	// "solemnity", or the 1962 form's "class-1".."class-4",
+	// "commemoration". The engine always supplies a rank: an unset or
+	// unrecognised rank on a sanctoral celebration defaults to "ferial"
+	// (calendar.buildCelebration), and every temporal-day constructor sets
+	// one explicitly. Consumers must not treat an empty Rank as meaning "no
+	// celebration".
+	Rank string
 }