fix(cv): enforce readable render palettes

Choose a contrasting header foreground for custom accents and keep public colour and font overrides inside safe supported values.

JobTrackerApi/Models/CvVariantSettings.cs

@@ -63,6 +63,16 @@ public sealed class CvCustomSectionSetting
 
 public static class CvVariantSettingsJson
 {
+    private static readonly HashSet<string> AllowedFonts = new(StringComparer.Ordinal)
+    {
+        "'Segoe UI', Roboto, Arial, sans-serif",
+        "Arial, Helvetica, sans-serif",
+        "Georgia, 'Times New Roman', serif",
+        "'Helvetica Neue', Arial, sans-serif",
+        "'Roboto', Arial, sans-serif",
+        "'Poppins', 'Segoe UI', Arial, sans-serif",
+    };
+
     private static readonly JsonSerializerOptions Options = new(JsonSerializerDefaults.Web)
     {
         PropertyNameCaseInsensitive = true,
@@ -83,9 +93,28 @@ public static class CvVariantSettingsJson
     {
         s ??= new CvVariantSettings();
         s.ThemeId = string.IsNullOrWhiteSpace(s.ThemeId) ? "modern" : s.ThemeId.Trim().ToLowerInvariant();
+        s.AccentColor = NormalizeColor(s.AccentColor);
+        s.HeadingFont = NormalizeFont(s.HeadingFont);
+        s.BodyFont = NormalizeFont(s.BodyFont);
         s.Sections ??= new();
         s.Overrides ??= new();
         s.CustomSections ??= new();
         return s;
     }
+
+    private static string? NormalizeColor(string? value)
+    {
+        var candidate = value?.Trim();
+        return candidate is { Length: 7 }
+            && candidate[0] == '#'
+            && candidate.Skip(1).All(Uri.IsHexDigit)
+                ? candidate.ToLowerInvariant()
+                : null;
+    }
+
+    private static string? NormalizeFont(string? value)
+    {
+        var candidate = value?.Trim();
+        return candidate is not null && AllowedFonts.Contains(candidate) ? candidate : null;
+    }
 }