localise chrome, smooth prose, in English and Bengali

The engine now owns the words it puts on a page that the author did not write
(ADR-0034). `internal/render/chrome.go` holds the phrase table, Gregorian month
names and decimal digits per language, keyed phrase-then-language so both forms
sit side by side and a half-translated row is visible while reading. Templates
reach it through `t`, `num` and `day`, registered before parsing so a site
override's blocks may call them too.

The reference theme stops hardcoding English: "Newer", "Page 2 of 2" and every
date now come from the table, while `datetime` attributes stay ASCII because a
parser reads them.

Authored text gets goldmark's typographer and nothing else — quotes, dashes and
ellipses smoothed, code spans untouched because it works on the parsed tree. It
is a parser option rather than a function over a page, so the transforms counter
does not move; state.md now says why, so the next reader does not miscount.

Deliberately absent: relative dates, which need a validity window that only the
cache entry will have, and body widow prevention, which cannot be done safely by
a pass over rendered HTML.

internal/render/chrome_test.go

@@ -0,0 +1,108 @@
+package render
+
+import (
+	"strings"
+	"testing"
+	"time"
+
+	"khosra/internal/content"
+)
+
+func TestChromeTextIsLocalisedAndNeverEmpty(t *testing.T) {
+	cases := []struct{ lang, key, want string }{
+		{"en", "newer", "Newer"},
+		{"bn", "newer", "নতুন"},
+		{"fr", "newer", "Newer"}, // unknown language falls back to the default locale
+		{"bn", "nope", "nope"},   // unknown phrase returns its key rather than nothing
+	}
+	for _, c := range cases {
+		if got := text(c.lang, c.key); got != c.want {
+			t.Errorf("text(%q, %q) = %q, want %q", c.lang, c.key, got, c.want)
+		}
+	}
+	if got := text("bn", "page-of", numerals("bn", 2), numerals("bn", 11)); got != "পৃষ্ঠা ২ / ১১" {
+		t.Errorf("page-of in Bengali = %q", got)
+	}
+	if got := text("en", "page-of", "2", "11"); got != "Page 2 of 11" {
+		t.Errorf("page-of in English = %q", got)
+	}
+}
+
+func TestEveryPhraseCarriesEveryLanguage(t *testing.T) {
+	// A phrase missing a language falls back silently, so nothing else would catch a half-translated table.
+	for key, forms := range chrome {
+		for lang := range months {
+			if forms[lang] == "" {
+				t.Errorf("phrase %q has no %s form", key, lang)
+			}
+		}
+	}
+	for lang, names := range months {
+		if len(names) != 12 {
+			t.Errorf("%s has %d month names, want 12", lang, len(names))
+		}
+	}
+	if len(digits["bn"]) != 10 {
+		t.Errorf("Bengali digits = %d, want 10", len(digits["bn"]))
+	}
+}
+
+func TestDatesReadInTheirOwnScript(t *testing.T) {
+	when := time.Date(2026, time.March, 8, 0, 0, 0, 0, time.UTC)
+	if got := day(content.DefaultLang, when); got != "8 March 2026" {
+		t.Errorf("English date = %q", got)
+	}
+	if got := day("bn", when); got != "৮ মার্চ ২০২৬" {
+		t.Errorf("Bengali date = %q, want Bengali digits and month", got)
+	}
+	if got := day("en", time.Time{}); got != "" {
+		t.Errorf("an undated bundle should render nothing, got %q", got)
+	}
+}
+
+func TestTypographerSmoothsProseAndLeavesCodeAlone(t *testing.T) {
+	r, err := New(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	b, err := content.Parse("posts/x.md", []byte(
+		"---\ntitle: X\n---\nShe said \"wait\" -- then left... `\"raw\" -- code`\n"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	out, err := r.Bundle(b, "en", nil, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := string(out)
+	for _, want := range []string{"“wait”", "–", "…"} {
+		if !strings.Contains(got, want) {
+			t.Errorf("prose missing %s:\n%s", want, got)
+		}
+	}
+	if !strings.Contains(got, `<code>&quot;raw&quot; -- code</code>`) {
+		t.Errorf("a code span must survive untouched:\n%s", got)
+	}
+}
+
+func TestMachineReadableOutputStaysASCII(t *testing.T) {
+	r, err := New(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	b, err := content.Parse("posts/x.bn.md", []byte("---\ntitle: এক\ndate: 2026-03-08\n---\n"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	out, err := r.Listing("posts", "bn", []content.Bundle{b}, 1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := string(out)
+	if !strings.Contains(got, `datetime="2026-03-08"`) {
+		t.Errorf("datetime must stay ASCII for parsers (ADR-0034):\n%s", got)
+	}
+	if !strings.Contains(got, "৮ মার্চ ২০২৬") {
+		t.Errorf("the visible date should read in Bengali:\n%s", got)
+	}
+}