fix-deviant(os): always reap the URL opener child process

Intentional deviation from Ghostty 1.3.1 (DEVIANT_FIXES.md row 32).
Zig's os/open.zig runs `try collectOutput(...)` before `wait()`: when
collection fails (e.g. a stream exceeds the 50 KiB limit), the error
returns early and the child is never waited for, leaving a zombie
process for the lifetime of Ghostty.

The Rust opener thread now always waits for the child (the pipes are
already closed at that point) and still logs the collection error.

Test Plan:
- cargo test -p ghostty-os open

crates/ghostty-os/src/open.rs

@@ -147,14 +147,18 @@ fn collect_output(child: &mut Child) -> io::Result<(Vec<u8>, Vec<u8>)> {
 }
 
 fn open_thread(mut child: Child) {
-    let stderr = match collect_output(&mut child) {
+    let collected = collect_output(&mut child);
+    // Zig's `try collectOutput` skips `wait` on error; reap anyway so the
+    // child does not stay a zombie (the pipes are closed by now).
+    let waited = child.wait();
+    let stderr = match collected {
         Ok((_stdout, stderr)) => stderr,
         Err(e) => {
             log::warn!("error collecting open command output err={e}");
             return;
         }
     };
-    if let Err(e) = child.wait() {
+    if let Err(e) = waited {
         log::warn!("error waiting for open command err={e}");
         return;
     }