i18n: make all UI chrome user-translatable via ui/<code>.ini

The interface chrome (version labels, TUI keybar/messages, CLI banner words,
web control labels, section-heading words) was English/Polish hardcoded in Go.
It is now data: the English and Polish tables ship as embedded lang/en.ini and
lang/pl.ini, and any language is user-overridable at <config>/ui/<code>.ini,
resolved per key with an English fallback. With ui_language = <code> plus a
names/<code>.ini, the WHOLE interface -- chrome, day names, saint names -- is
translatable without a rebuild.

- i18n.Get loads the embedded English baseline, overlays the embedded/user
  language file, caches per lang; field <-> INI-key mapping is by reflection
  (lang.go) so the tables and files stay in sync automatically. Edge-space
  values (e.g. "error: ") are double-quoted so the INI trim keeps them. The
  Go tables move to golden_test.go; TestGoldenMatchesEmbedded asserts the
  embedded files still parse back to them, and TestGenerateLangFiles
  regenerates them (LECTIO_GEN=1).
- config.UIDir(); wire i18n.SetUserDir in the CLI, TUI and web entry points.
- README/config: document ui/<code>.ini alongside names/<code>.ini.

1 files changed, 14 insertions, 1 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index c9a00f2..08c0b60 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       any code (en, pl, ...)   (chrome is en/pl, else English; day/saint names from names/<code>.ini)
+#   ui_language       any code (en, pl, ...)   (chrome from ui/<code>.ini, day names from names/<code>.ini; en/pl built in, else English)
 #   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)
@@ -347,6 +347,19 @@ func CorporaDir() (string, error) {
 	return filepath.Join(filepath.Dir(p), "corpora"), nil
 }
 
+// UIDir is the user directory for drop-in UI-chrome language files
+// (<code>.ini: button/label/keybar strings), alongside names/, calendars/ and
+// corpora/ under the lectio config dir. A file here overrides the built-in
+// chrome for its language key by key; with ui_language = <code> it translates
+// the whole interface without a rebuild. Mirrors NamesDir.
+func UIDir() (string, error) {
+	p, _, err := configPath()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(filepath.Dir(p), "ui"), 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;