cmd/run.ts: launch SumatraPDF detached, don't wait for it to exit

Bun keeps the script alive until a spawned child exits, so `bun cmd/run.ts`
hung until SumatraPDF was closed. unref() the subprocess (and ignore its
stdio) so the script returns as soon as the app is launched.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: kjk

cmd/run.ts

@@ -27,9 +27,14 @@ async function main() {
   console.log(`build took ${elapsed}s`);
 
   const path = join("out", "dbg64", "SumatraPDF-dll.exe");
-  Bun.spawn([path], {
+  // launch and detach: don't keep this script alive waiting for SumatraPDF to exit
+  const proc = Bun.spawn([path], {
     cwd: ".",
+    stdin: "ignore",
+    stdout: "ignore",
+    stderr: "ignore",
   });
+  proc.unref();
 }
 
 await main();