[TUI] Update request-count test for response records introduced by #39372

Summary

The TUI test changing_directory_preserves_project_trust_permissions_history_and_hooks fails after #39372 (8843960ba06b1b2570e689f3fff354c324ab2417).

Reproduction

Run:

cargo test -p codex-tui --lib app::tests::session_lifecycle_requests::changing_directory_preserves_project_trust_permissions_history_and_hooks -- --exact

The test reaches the assertion in codex-rs/tui/src/app/tests/session_lifecycle_requests.rs where it counts recorded requests, and observes one request where zero are expected.

Cause

#39372 changed the app-server test recorder to store JSON-RPC responses in the same collection as outbound requests, using the synthetic method server/request/response. The test still treats the collection length as the number of outbound app-server requests, so responses inflate the count.

Suggested fix

Exclude records whose method is server/request/response from this count, or keep recorded responses in a separate collection. The former is the smallest targeted change and preserves the existing test intent.