naming: localise liturgical day names in any language

Add internal/naming, which renders temporal day names and celebration
display names from the calendar engine's slugs in any language. English is
the built-in baseline; a language is data -- an embedded lang/<code>.ini
(pl shipped) and/or a user file at <config dir>/names/<code>.ini that
overrides it key by key. Names compose from a small vocabulary plus
per-language format templates, so word order and grammatical case can
differ (e.g. Polish genitive "3. Niedziela Okresu Zwykłego"); any string a
language omits falls back to English.

- Move day-name generation out of calendar (calendar.HumanizeSlug removed,
  calendar stays a pure engine) into naming.DayName; the English golden
  cases carry over verbatim.
- naming.CelebrationName unifies the three duplicated resolvers
  (cli/readings/calfeed): name.<lang> -> English -> Latin -> humanized slug.
  Saint names stay in the calendar data (name.<lang>), overridable via
  calendar layers.
- config: ui_language now accepts any code (lower-cased, not clamped to
  en/pl) so names/<code>.ini applies; UI chrome still resolves en/pl and
  falls back to English. Add NamesDir(); wire naming.SetUserDir (and the
  previously unwired bible.SetUserCorporaDir) in the TUI and web mains too,
  so external corpora and name files work across all three binaries.

1 files changed, 4 insertions, 17 deletions

diff --git a/internal/readings/offline.go b/internal/readings/offline.go
index 566fc7a..d0b8942 100644
--- a/internal/readings/offline.go
+++ b/internal/readings/offline.go
@@ -9,6 +9,7 @@ import (
 	"github.com/lukaszkasprzak/lectio/internal/calendar"
 	"github.com/lukaszkasprzak/lectio/internal/config"
 	"github.com/lukaszkasprzak/lectio/internal/liturgy"
+	"github.com/lukaszkasprzak/lectio/internal/naming"
 )
 
 // offlineLoad resolves a day's readings entirely from the embedded calendar
@@ -119,22 +120,8 @@ func dayInfo(cfg config.Config, day calendar.LiturgicalDay) liturgy.DayInfo {
 }
 
 // celebrationName is the observed celebration's name in the UI language,
-// falling back to English then a humanized slug for temporal days that carry no
-// proper name (mirrors the CLI's cli.celebrationName). An empty result omits
-// the header line.
+// resolved by naming.CelebrationName (name.<lang> -> English -> Latin ->
+// humanized slug). An empty result (unnamed feria) omits the header line.
 func celebrationName(cfg config.Config, c calendar.Celebration) string {
-	lang := "en"
-	if cfg.UILanguage == "pl" {
-		lang = "pl"
-	}
-	if n := c.Name[lang]; n != "" {
-		return n
-	}
-	if n := c.Name["en"]; n != "" {
-		return n
-	}
-	if c.Slug == "" {
-		return ""
-	}
-	return calendar.HumanizeSlug(c.Slug)
+	return naming.CelebrationName(cfg.UILanguage, c)
 }