fix(webmcp): add serde_json to integration_tests Bazel deps

The integration test calls serde_json::to_string_pretty() directly.
Cargo resolves it transitively, but Bazel requires explicit deps.
Fixes Bazel Test arm64-darwin/linux compilation failure.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dfinityianblenke

rs/webmcp/codegen/BUILD.bazel

@@ -65,5 +65,8 @@ rust_test(
         # Note: management_canister_types/tests/ic.did is not publicly exported;
         # the integration test skips it gracefully when not present.
     ],
-    deps = [":ic_webmcp_codegen"] + DEV_DEPENDENCIES,
+    deps = [
+        ":ic_webmcp_codegen",
+        "@crate_index//:serde_json",
+    ] + DEV_DEPENDENCIES,
 )