refactor(calendar): Rank int enum -> unified string token (OF unchanged, oracle 0 mismatches)

Adds EF rank constants (class-1..4, commemoration); ofRankOrder() for the two
ordered comparisons; buildCelebration defaults missing rank to ferial.

2 files changed, 39 insertions, 8 deletions

diff --git a/internal/calendar/calendar.go b/internal/calendar/calendar.go
index 3465182..98dec43 100644
--- a/internal/calendar/calendar.go
+++ b/internal/calendar/calendar.go
@@ -26,10 +26,10 @@ func Compute(date time.Time, sel Selection, layers []Layer) LiturgicalDay {
 		}
 		// On band-2 privileged days only solemnities survive (and they transfer);
 		// on Sundays (band 6) only feasts and solemnities compete.
-		if td.Privileged && cel.Rank < RankSolemnity {
+		if td.Privileged && ofRankOrder(cel.Rank) < ofRankOrder(RankSolemnity) {
 			continue
 		}
-		if td.Sunday && cel.Rank < RankFeast {
+		if td.Sunday && ofRankOrder(cel.Rank) < ofRankOrder(RankFeast) {
 			continue
 		}
 		effective := transferIfImpeded(cel, when, sel)
@@ -105,6 +105,9 @@ func buildCelebration(slug string, rc RawCelebration) Celebration {
 			c.Name[strings.TrimPrefix(k, "name.")] = v
 		}
 	}
+	if c.Rank == "" {
+		c.Rank = RankFerial
+	}
 	if m := massFrom(rc.Fields); len(m.Readings) > 0 {
 		c.Masses = append(c.Masses, m)
 	}
diff --git a/internal/calendar/types.go b/internal/calendar/types.go
index 77d57ab..0ccef8b 100644
--- a/internal/calendar/types.go
+++ b/internal/calendar/types.go
@@ -4,16 +4,44 @@ package calendar
 
 import "time"
 
-type Rank int
+// Rank is a form-specific rank token. Ordinary Form uses the values below;
+// the Extraordinary Form uses its own (class-1..class-4, commemoration, ferial).
+// Each form's precedence interprets its own vocabulary.
+type Rank string
 
 const (
-	RankFerial   Rank = iota // ordinary weekday
-	RankOptional             // optional memorial
-	RankMemorial             // obligatory memorial
-	RankFeast
-	RankSolemnity
+	// Ordinary Form ranks.
+	RankFerial    Rank = "ferial"    // ordinary weekday
+	RankOptional  Rank = "optional"  // optional memorial
+	RankMemorial  Rank = "memorial"  // obligatory memorial
+	RankFeast     Rank = "feast"     //
+	RankSolemnity Rank = "solemnity" //
+
+	// Extraordinary Form ranks (1960 Code of Rubrics): I-IV class + commemoration.
+	RankClass1        Rank = "class-1"
+	RankClass2        Rank = "class-2"
+	RankClass3        Rank = "class-3"
+	RankClass4        Rank = "class-4"
+	RankCommemoration Rank = "commemoration"
 )
 
+// ofRankOrder orders the Ordinary Form ranks for the few `<` comparisons in the
+// OF path (ferial lowest, solemnity highest). Unknown/empty → 0 (ferial-level).
+func ofRankOrder(r Rank) int {
+	switch r {
+	case RankSolemnity:
+		return 4
+	case RankFeast:
+		return 3
+	case RankMemorial:
+		return 2
+	case RankOptional:
+		return 1
+	default:
+		return 0
+	}
+}
+
 type Class int
 
 const (