Gate set_executable_permissions call with #[cfg(unix)]

The method is cfg(unix) but the call site wasn't gated, causing a
compile error on Windows.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/sidecar/mod.rs

@@ -339,6 +339,7 @@ impl SidecarManager {
             Err(e) if e.raw_os_error() == Some(13) => {
                 // Permission denied — fix permissions and retry once
                 eprintln!("[sidecar-rs] Permission denied, fixing permissions and retrying...");
+                #[cfg(unix)]
                 if let Some(dir) = path.parent() {
                     Self::set_executable_permissions(dir);
                 }