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, 28 insertions, 0 deletions

diff --git a/internal/i18n/override_test.go b/internal/i18n/override_test.go
new file mode 100644
index 0000000..bac5e2c
--- /dev/null
+++ b/internal/i18n/override_test.go
@@ -0,0 +1,28 @@
+package i18n
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestUserOverridePartialAndMap(t *testing.T) {
+	dir := t.TempDir()
+	os.WriteFile(filepath.Join(dir, "fr.ini"),
+		[]byte("banner_gospel = Évangile\nversion.vul = Vulgate (latin)\n"), 0o644)
+	SetUserDir(dir)
+	t.Cleanup(func() { SetUserDir("") })
+	u := Get("fr")
+	if u.BannerGospel != "Évangile" {
+		t.Errorf("scalar override: BannerGospel = %q", u.BannerGospel)
+	}
+	if u.Version["vul"] != "Vulgate (latin)" {
+		t.Errorf("map override: version.vul = %q", u.Version["vul"])
+	}
+	if u.Version["drb"] != "Douay-Rheims (English)" {
+		t.Errorf("map fallback: version.drb = %q (want English baseline)", u.Version["drb"])
+	}
+	if u.BannerReadings != "Readings" {
+		t.Errorf("scalar fallback: BannerReadings = %q (want English)", u.BannerReadings)
+	}
+}