fix(macos-container): preflight check for container system service

Fail early with a clear message when the Apple Container system service
isn't running, instead of surfacing an opaque XPC connection error mid-build.

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

bot_bottle/backend/macos_container/util.py

@@ -35,6 +35,20 @@ def require_container() -> None:
         info("Apple Container is required but was not found on PATH.")
         info("Install: https://github.com/apple/container/releases")
         die("container not found")
+    _require_container_service()
+
+
+def _require_container_service() -> None:
+    result = subprocess.run(
+        [_CONTAINER, "system", "info"],
+        stdout=subprocess.DEVNULL,
+        stderr=subprocess.DEVNULL,
+        check=False,
+    )
+    if result.returncode != 0:
+        info("Apple Container system service is not running.")
+        info("Start it with: container system start")
+        die("container system service not running")
 
 
 def dns_server() -> str: