fix(appd): set WEFT_DISABLE_CGROUP in supervisor test

In environments where XDG_RUNTIME_DIR/systemd/private exists but the
user systemd session is not functional, systemd_cgroup_available()
returns true and the test script is wrapped with systemd-run, which
fails immediately, causing ChildStdout to return EOF before READY.

Set WEFT_DISABLE_CGROUP=1 for the duration of the test and restore
it on exit.

crates/weft-appd/src/main.rs

@@ -813,8 +813,12 @@ mod tests {
         std::fs::set_permissions(&script, std::fs::Permissions::from_mode(0o755)).unwrap();
 
         let prior = std::env::var("WEFT_RUNTIME_BIN").ok();
+        let prior_cgroup = std::env::var("WEFT_DISABLE_CGROUP").ok();
         // SAFETY: single-threaded test (flavor = "current_thread"); no concurrent env access.
-        unsafe { std::env::set_var("WEFT_RUNTIME_BIN", &script) };
+        unsafe {
+            std::env::set_var("WEFT_RUNTIME_BIN", &script);
+            std::env::set_var("WEFT_DISABLE_CGROUP", "1");
+        }
 
         let registry: Registry = Arc::new(Mutex::new(SessionRegistry::default()));
         let mut rx = registry.lock().await.subscribe();
@@ -856,6 +860,10 @@ mod tests {
                 Some(v) => std::env::set_var("WEFT_RUNTIME_BIN", v),
                 None => std::env::remove_var("WEFT_RUNTIME_BIN"),
             }
+            match prior_cgroup {
+                Some(v) => std::env::set_var("WEFT_DISABLE_CGROUP", v),
+                None => std::env::remove_var("WEFT_DISABLE_CGROUP"),
+            }
         }
     }