fix invisible text for colors without an alpha channel

FrosFont.flush passed colors to AWT as RGBA, so vanilla-style rgb
constants like 0x55FF55 got alpha 0 and drew fully transparent - this
made the Armor HUD's durability percentages (green/yellow/red) never
show. Alpha-less colors now draw opaque, matching vanilla's own
treatment of ChatFormatting-style colors.

src/main/java/cc/fros/util/render/FrosFont.java

@@ -414,7 +414,11 @@ public final class FrosFont {
     private static int flush(Graphics2D graphics, String text, int start, int end, int cursor, int color, int baseline) {
         if (end <= start) return cursor;
         String segment = text.substring(start, end);
-        graphics.setColor(new Color(color, true));
+        // rgb colors without an alpha channel (0x55FF55, like vanilla's own
+        // formatting codes) draw opaque, matching vanilla's rule of treating
+        // a missing alpha as 255 instead of rendering invisible text
+        int argb = (color & 0xFF000000) == 0 ? 0xFF000000 | color : color;
+        graphics.setColor(new Color(argb, true));
         graphics.drawString(segment, cursor, baseline);
         return cursor + metrics.stringWidth(segment);
     }