Add page <title> to every rendered page

layout.html now emits <title>{{ pageTitle . }} · Palette</title>; the
pageTitle template func maps the Page field to a label (New paste,
Public pastes, Saved, Settings, paste title or 'Paste <id>', Unlock,
Can, Not found).

internal/web/web.go

@@ -74,6 +74,7 @@ func New() (*UI, error) {
 		"humanSize":   humanSize,
 		"version":     func() string { return Version },   // #93: topbar version label
 		"defaultDark": func() bool { return DefaultDark }, // #127: server-configured default
+		"pageTitle":   pageTitle,                          // page <title> labels
 	}
 	t, err := template.New("").Funcs(funcs).ParseFS(tmplFS, "templates/*.html")
 	if err != nil {
@@ -82,6 +83,38 @@ func New() (*UI, error) {
 	return &UI{tmpl: t}, nil
 }
 
+// pageTitle returns the <title> label for the rendered page. Page data is
+// always a map with a "Page" key set by the handlers.
+func pageTitle(data any) string {
+	m, _ := data.(map[string]any)
+	page, _ := m["Page"].(string)
+	id, _ := m["ID"].(string)
+	title, _ := m["Title"].(string)
+	switch page {
+	case "new":
+		return "New paste"
+	case "public":
+		return "Public pastes"
+	case "saved":
+		return "Saved"
+	case "settings":
+		return "Settings"
+	case "paste":
+		if title != "" {
+			return title
+		}
+		return "Paste " + id
+	case "unlock":
+		return "Unlock " + id
+	case "can":
+		return "Can " + id
+	case "notfound":
+		return "Not found"
+	default:
+		return "Palette"
+	}
+}
+
 func humanSize(n int) string {
 	if n < 1024 {
 		return fmt.Sprintf("%d B", n)