fix: use safe docker bind mount syntax for sandbox mounts (#1655)

Docker's -v host:container syntax is ambiguous for Windows drive-letter
paths (e.g. D:/...) because ':' is both the drive separator and the
volume separator, causing mount failures on Windows hosts.

Introduce _format_container_mount() which uses '--mount type=bind,...'
for Docker (unambiguous on all platforms) and keeps '-v' for Apple
Container runtime which does not support the --mount flag yet.

Adds unit tests covering Windows paths, read-only mounts, and Apple
Container pass-through.

Made-with: Cursor

backend/tests/test_aio_sandbox_local_backend.py

@@ -0,0 +1,28 @@
+from deerflow.community.aio_sandbox.local_backend import _format_container_mount
+
+
+def test_format_container_mount_uses_mount_syntax_for_docker_windows_paths():
+    args = _format_container_mount("docker", "D:/deer-flow/backend/.deer-flow/threads", "/mnt/threads", False)
+
+    assert args == [
+        "--mount",
+        "type=bind,src=D:/deer-flow/backend/.deer-flow/threads,dst=/mnt/threads",
+    ]
+
+
+def test_format_container_mount_marks_docker_readonly_mounts():
+    args = _format_container_mount("docker", "/host/path", "/mnt/path", True)
+
+    assert args == [
+        "--mount",
+        "type=bind,src=/host/path,dst=/mnt/path,readonly",
+    ]
+
+
+def test_format_container_mount_keeps_volume_syntax_for_apple_container():
+    args = _format_container_mount("container", "/host/path", "/mnt/path", True)
+
+    assert args == [
+        "-v",
+        "/host/path:/mnt/path:ro",
+    ]