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, 12 insertions, 0 deletions

diff --git a/internal/calendar/types.go b/internal/calendar/types.go
index 298e49d..6d828f1 100644
--- a/internal/calendar/types.go
+++ b/internal/calendar/types.go
@@ -17,6 +17,18 @@ const (
 	RankFeast     Rank = "feast"     //
 	RankSolemnity Rank = "solemnity" //
 
+	// RankSunday is a DISPLAY-ONLY rank: in the 1969 Universal Norms' Table of
+	// Liturgical Days, Sunday is its own category, never a solemnity (Sundays
+	// of Christmas Time/Ordinary Time are band 6, below feasts of the Lord;
+	// Sundays of Advent/Lent/Easter are band 2, above solemnities -- a flat
+	// Rank cannot express both bands, and this constant does not try to).
+	// Nothing in this package ever assigns it to Celebration.Rank, and it MUST
+	// NOT be added to ofRankOrder below: ofRankOrder's default case (0,
+	// ferial-level) would make every Sunday lose every precedence contest.
+	// Callers that want it derive it themselves from the already-computed,
+	// unchanged Celebration (see internal/readings/offline.go's displayRank).
+	RankSunday Rank = "sunday"
+
 	// Extraordinary Form ranks (1960 Code of Rubrics): I-IV class + commemoration.
 	RankClass1        Rank = "class-1"
 	RankClass2        Rank = "class-2"