Cargo.lock: png as a direct dependency

Standalone re-resolve (seeded from the workspace root lock) after the
icon module added png; the crate was already pinned transitively, so
the only delta is the direct-dep listing.

Co-Authored-By: Claude <[email protected]>

 Cargo.lock | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Cargo.lock b/Cargo.lock
index 34acb53..00d3f58 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -355,6 +355,7 @@ dependencies = [
  "libc",
  "log",
  "naga",
+ "png",
  "raw-window-handle",
  "resvg",
  "rfd",