calendar/readings: report Sunday as its own display rank, not solemnity

The Ordinary Form's Table of Liturgical Days treats Sunday as its own
category, never a solemnity. temporal.go's sundayDay() already marks these
days distinctly from named solemnities (Class stays unset, unlike solemn()'s
ClassLord); internal/readings/offline.go now reads that existing signal to
relabel the REPORTED rank to "sunday" for ordinary and privileged-season
Sundays alike, leaving Celebration.Rank, ofRankOrder and all precedence
untouched. Named solemnities landing on a Sunday (Easter, Pentecost, ...)
and feasts of the Lord (Holy Family) keep reporting their own rank. The 1962
form is untouched.

Added calendar.RankSunday (display-only, deliberately excluded from
ofRankOrder), the i18n Sunday/niedziela words, and a test pinning the exact
dates from the original bug report.

4 files changed, 7 insertions, 5 deletions

diff --git a/internal/i18n/golden_test.go b/internal/i18n/golden_test.go
index b32a259..d06d63b 100644
--- a/internal/i18n/golden_test.go
+++ b/internal/i18n/golden_test.go
@@ -27,7 +27,7 @@ var enUI = UI{
 	},
 	Rank: map[string]string{
 		"solemnity": "solemnity", "feast": "feast", "memorial": "memorial",
-		"optional": "optional memorial", "ferial": "feria",
+		"optional": "optional memorial", "ferial": "feria", "sunday": "Sunday",
 		"class-1": "I class", "class-2": "II class",
 		"class-3": "III class", "class-4": "IV class",
 		"commemoration": "commemoration",
@@ -125,7 +125,7 @@ var plUI = UI{
 	Rank: map[string]string{
 		"solemnity": "uroczystość", "feast": "święto",
 		"memorial": "wspomnienie obowiązkowe", "optional": "wspomnienie dowolne",
-		"ferial":  "dzień powszedni",
+		"ferial": "dzień powszedni", "sunday": "niedziela",
 		"class-1": "I klasy", "class-2": "II klasy",
 		"class-3": "III klasy", "class-4": "IV klasy",
 		"commemoration": "komemoracja",
diff --git a/internal/i18n/lang/en.ini b/internal/i18n/lang/en.ini
index 60a5f32..4abd5d1 100644
--- a/internal/i18n/lang/en.ini
+++ b/internal/i18n/lang/en.ini
@@ -19,6 +19,7 @@ rank.ferial = feria
 rank.memorial = memorial
 rank.optional = optional memorial
 rank.solemnity = solemnity
+rank.sunday = Sunday
 footer_keys = tab/⇧tab version  ←/→ day  d date  j/k scroll  space/b page  g/G top/bottom  q quit
 loading = loading…
 no_readings_for = "no readings for "
diff --git a/internal/i18n/lang/pl.ini b/internal/i18n/lang/pl.ini
index 5991938..4ae4ebf 100644
--- a/internal/i18n/lang/pl.ini
+++ b/internal/i18n/lang/pl.ini
@@ -19,6 +19,7 @@ rank.ferial = dzień powszedni
 rank.memorial = wspomnienie obowiązkowe
 rank.optional = wspomnienie dowolne
 rank.solemnity = uroczystość
+rank.sunday = niedziela
 footer_keys = tab/⇧tab wersja  ←/→ dzień  d data  j/k przewiń  spacja/b strona  g/G góra/dół  q wyjście
 loading = ładowanie…
 no_readings_for = "brak czytań na "
diff --git a/internal/i18n/vocab_test.go b/internal/i18n/vocab_test.go
index 97c09d6..d0fd603 100644
--- a/internal/i18n/vocab_test.go
+++ b/internal/i18n/vocab_test.go
@@ -12,7 +12,7 @@ import (
 func TestVocabularyCoversEveryConstant(t *testing.T) {
 	ranks := []calendar.Rank{
 		calendar.RankFerial, calendar.RankOptional, calendar.RankMemorial,
-		calendar.RankFeast, calendar.RankSolemnity,
+		calendar.RankFeast, calendar.RankSolemnity, calendar.RankSunday,
 		calendar.RankClass1, calendar.RankClass2, calendar.RankClass3,
 		calendar.RankClass4, calendar.RankCommemoration,
 	}
@@ -31,7 +31,7 @@ func TestVocabularyCoversEveryConstant(t *testing.T) {
 func TestEnglishRankWordingUnchanged(t *testing.T) {
 	want := map[string]string{
 		"solemnity": "solemnity", "feast": "feast", "memorial": "memorial",
-		"optional": "optional memorial", "ferial": "feria",
+		"optional": "optional memorial", "ferial": "feria", "sunday": "Sunday",
 		"class-1": "I class", "class-2": "II class",
 		"class-3": "III class", "class-4": "IV class",
 		"commemoration": "commemoration",
@@ -53,7 +53,7 @@ func TestPolishRankWordingUnchanged(t *testing.T) {
 	want := map[string]string{
 		"solemnity": "uroczystość", "feast": "święto",
 		"memorial": "wspomnienie obowiązkowe", "optional": "wspomnienie dowolne",
-		"ferial":  "dzień powszedni",
+		"ferial": "dzień powszedni", "sunday": "niedziela",
 		"class-1": "I klasy", "class-2": "II klasy",
 		"class-3": "III klasy", "class-4": "IV klasy",
 		"commemoration": "komemoracja",