chore(theme): re-vendor cms theme copies after nav-link and rem-first fixes

Picks up the post-title/post-lede selectors, the narrowed .bn-nav-link
selector, the rem-first default base size and ParseFontSizeBase.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

internal/theme/css.go

@@ -148,10 +148,12 @@ func writeTypographyVars(css *strings.Builder, typography *ThemeTypography) {
 
 var fontSizeOverrideSelectors = map[string]string{
 	"h1": "h1", "h2": "h2", "h3": "h3", "h4": "h4", "h5": "h5", "h6": "h6",
-	"nav-link":         ".bn-navbar a",
+	"nav-link":         ".bn-nav-link",
 	"hero-title":       ".bn-hero-title",
 	"hero-subtitle":    ".bn-hero-subtitle",
 	"index-card-title": ".bn-post-card-title",
+	"post-title":       ".bn-post-title",
+	"post-lede":        ".bn-post-lede",
 }
 
 var headingOverrideKeys = map[string]bool{"h1": true, "h2": true, "h3": true, "h4": true, "h5": true, "h6": true}

internal/theme/defaults.go

@@ -49,7 +49,7 @@ func DefaultTheme() *Theme {
 			FontHeading:    "system",
 			FontBody:       "system",
 			FontMono:       "system",
-			FontSizeBase:   "16",
+			FontSizeBase:   "1rem",
 			LineHeightBase: "1.5",
 			FontWeightBase: "normal",
 		},

internal/theme/fontsize.go

@@ -53,21 +53,29 @@ func ValidateFontSize(v string) error {
 	return nil
 }
 
-// NormalizeFontSizeBase upgrades legacy bare px numbers ("16") to "16px" and
-// validates unit-suffixed values. Returns "" for anything invalid so bad
-// stored data degrades to the CSS fallback instead of breaking the sheet.
-func NormalizeFontSizeBase(v string) string {
+// ParseFontSizeBase normalizes a stored base font size and validates
+// unit-suffixed values.
+func ParseFontSizeBase(v string) (string, error) {
 	v = strings.TrimSpace(v)
 	if v == "" {
-		return ""
+		return "", nil
 	}
+	// Legacy bare numbers were never consumed by any stylesheet, so they are
+	// normalized to the 1rem default rather than resurrected as a real size.
 	if _, err := strconv.ParseFloat(v, 64); err == nil {
-		v += "px"
+		v = "1rem"
 	}
 	if err := ValidateFontSize(v); err != nil {
-		return ""
+		return "", err
 	}
-	return v
+	return v, nil
+}
+
+// NormalizeFontSizeBase returns "" for anything invalid so bad stored data
+// degrades to the CSS fallback instead of breaking the sheet.
+func NormalizeFontSizeBase(v string) string {
+	out, _ := ParseFontSizeBase(v)
+	return out
 }
 
 // SanitizeFontSizeOverrides drops empty values, rejects unknown keys and