ww source: align UTF-8 BOM placement

internal/wwpackage/package.ww

@@ -724,7 +724,12 @@ fn pkgskipspace(src: str, start: i32) i32 = {
 };
 
 fn pkgclause(src: str, out: *str) bool = {
-	let i: i32 = pkgskipspace(src, 0);
+	// Match the compiler readers: one UTF-8 BOM is invisible only at the
+	// first raw source position. The full stage driver owns later-BOM errors.
+	let start: i32 = 0;
+	if (src.len >= 3 && src[0] == 0xefu8 && src[1] == 0xbbu8
+	    && src[2] == 0xbfu8) { start = 3; };
+	let i: i32 = pkgskipspace(src, start);
 	let word: str = "package";
 	if (i + word.len >= src.len) { return false; };
 	let j: i32 = 0;