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.

2 files changed, 28 insertions, 19 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index 299c942..c9a00f2 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -37,7 +37,7 @@ const configHeader = `# lectio configuration (INI). Full-line comments only (# o
 #   width             integer; 0 = detect terminal width
 #   all               true | false             (all readings, or just the gospel)
 #   offline           true | false             (never fetch; cache/sigla only)
-#   ui_language       en | pl                  (interface chrome; readings stay source-language)
+#   ui_language       any code (en, pl, ...)   (chrome is en/pl, else English; day/saint names from names/<code>.ini)
 #   reading_lang      language for offline reading text (e.g. en, pl); blank follows ui_language
 #   reading_version   force a specific bible corpus code (e.g. drb, wuj); blank = auto-resolve
 #   sigla_style       auto | polish | english | latin  (citation dialect; auto follows ui_language)
@@ -131,21 +131,14 @@ func NormalizeDisplay(display string) string {
 	return d
 }
 
-// validUILanguages are the two UI chrome languages lectio understands.
-var validUILanguages = map[string]bool{
-	"en": true,
-	"pl": true,
-}
-
-// NormalizeUILanguage lower-cases lang and falls back to "en" when it is not
-// one of validUILanguages -- the same lenient style as NormalizeDisplay (no
-// error, just a safe default).
+// NormalizeUILanguage lower-cases and trims a ui_language code. Any code is
+// accepted: it selects day- and saint-name localisation (names/<code>.ini, via
+// internal/naming) and, for the UI chrome, resolves through i18n.Get, which
+// falls back to English for anything other than the built-in "en"/"pl". So a
+// user can set ui_language = fr, ship a names/fr.ini, and get French day names
+// with English chrome -- no rebuild.
 func NormalizeUILanguage(lang string) string {
-	l := strings.ToLower(lang)
-	if !validUILanguages[l] {
-		return "en"
-	}
-	return l
+	return strings.ToLower(strings.TrimSpace(lang))
 }
 
 // NormalizeSiglaStyle maps a sigla_style setting to one of "auto", "polish",
@@ -354,6 +347,19 @@ func CorporaDir() (string, error) {
 	return filepath.Join(filepath.Dir(p), "corpora"), nil
 }
 
+// NamesDir is the user directory for drop-in day-name language files
+// (<code>.ini), alongside calendars/ and corpora/ under the lectio config dir.
+// A file here overrides the built-in day names for its language key by key;
+// combined with ui_language = <code>, it localises the daily view to any
+// language without a rebuild. Mirrors CalendarsDir/CorporaDir.
+func NamesDir() (string, error) {
+	p, _, err := configPath()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(filepath.Dir(p), "names"), nil
+}
+
 // BooksPath returns the path to the optional user books.ini (in the same
 // directory as the config file). There is no embedded seed on disk -- absence
 // means "use the built-in defaults".
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index 1035426..dd75808 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -169,18 +169,21 @@ func TestUILanguageLoadsPL(t *testing.T) {
 	}
 }
 
-func TestUILanguageNormalizesUnknown(t *testing.T) {
+func TestUILanguagePreservesAnyCode(t *testing.T) {
+	// Any ui_language code is kept (lower-cased): it drives day/saint-name
+	// localisation via names/<code>.ini. The UI chrome, resolved through
+	// i18n.Get, still falls back to English for a code it has no table for.
 	dir := t.TempDir()
 	t.Setenv("XDG_CONFIG_HOME", dir)
 	os.MkdirAll(filepath.Join(dir, "lectio"), 0o755)
 	os.WriteFile(filepath.Join(dir, "lectio", "config.toml"),
-		[]byte("ui_language = \"bogus\"\n"), 0o644)
+		[]byte("ui_language = \"FR\"\n"), 0o644)
 	cfg, err := Load()
 	if err != nil {
 		t.Fatal(err)
 	}
-	if cfg.UILanguage != "en" {
-		t.Errorf("UILanguage = %q, want %q (normalized from bogus)", cfg.UILanguage, "en")
+	if cfg.UILanguage != "fr" {
+		t.Errorf("UILanguage = %q, want %q (lower-cased, not clamped)", cfg.UILanguage, "fr")
 	}
 }