chore: init env_logger in --thumbnail mode

RUST_LOG on the thumbnailer now surfaces cce-ui's device/tier logs
(which Vulkan device, whether the ray-query tier engaged) — the
diagnostic surface for CCE_VK_DEVICE runs.

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01G5djCURa3LVnRU8WacanLC

 src/main.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/main.rs b/src/main.rs
index 74016fc..33dfc4d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -60,6 +60,7 @@ fn main() {
     // Headless thumbnail mode: no Wayland, no window — render and exit.
     //   cce-designer --thumbnail <project-dir-or-state.json> <out.png> [--size N]
     if let Some(i) = args.iter().position(|a| a == "--thumbnail") {
+        let _ = env_logger::try_init();
         let (Some(project), Some(out)) = (args.get(i + 1), args.get(i + 2)) else {
             eprintln!("usage: cce-designer --thumbnail <project> <out.png> [--size N]");
             std::process::exit(2);