Fix the release build: skip windows metadata when cross-compiling

`bun build --compile --target=bun-windows-x64` rejects `--windows-title` unless
the host is Windows:

    error: Using --windows-title is only available when compiling on Windows
    build failed for windows-x64 (exit 1)

CI releases all five targets from one Ubuntu runner, so the flag failed the
release on the last of the five builds — after the other four had already been
produced. Locally on Windows it passed, which is why it shipped.

The metadata is now stamped only on a Windows host. The published binary goes
without it rather than the release failing.

Extracted `buildArgs()` so the host-dependent branch is testable: the previous
version could only be checked by running a five-platform build on two operating
systems.

scripts/release.ts

@@ -20,6 +20,26 @@ export const TARGETS: Target[] = [
 
 const OUT = 'dist/release';
 
+/**
+ * Build arguments for one target.
+ *
+ * Executable metadata can only be stamped by a Windows host: bun rejects
+ * `--windows-title` when cross-compiling, and CI releases every target from one
+ * Ubuntu runner. The published binary goes without it rather than the release
+ * failing on the last of five builds.
+ */
+export function buildArgs(t: Target, outfile: string, host = process.platform): string[] {
+  const args = ['build', '--compile', '--minify', `--target=${t.target}`, 'src/cli.tsx', '--outfile', outfile];
+  if (t.windows && host === 'win32') {
+    args.push(
+      '--windows-title=shiro-neko',
+      '--windows-description=Agentic coding CLI',
+      `--windows-version=${VERSION.split('-')[0]}.0`,
+    );
+  }
+  return args;
+}
+
 /**
  * Builds one executable per platform.
  *
@@ -58,16 +78,7 @@ async function main(): Promise<void> {
     const base = `shiro-${t.name}`;
     const outfile = join(OUT, base);
 
-    const buildArgs = ['build', '--compile', '--minify', `--target=${t.target}`, 'src/cli.tsx', '--outfile', outfile];
-    if (t.windows) {
-      buildArgs.push(
-        '--windows-title=shiro-neko',
-        '--windows-description=Agentic coding CLI',
-        `--windows-version=${VERSION.split('-')[0]}.0`,
-      );
-    }
-
-    const proc = Bun.spawn(['bun', ...buildArgs], { stdout: 'inherit', stderr: 'inherit' });
+    const proc = Bun.spawn(['bun', ...buildArgs(t, outfile)], { stdout: 'inherit', stderr: 'inherit' });
     const code = await proc.exited;
     if (code !== 0) {
       console.error(`\nbuild failed for ${t.name} (exit ${code})`);