fix(tests): use portpicker for ephemeral port in default_role_integration_test

[AlexMikhalev]

Summary

• Replaces hardcoded port 8085 in terraphim_server/tests/default_role_integration_test.rs with portpicker::pick_unused_port().
• portpicker is already a crate dependency (in [dependencies], used by tests/server.rs).
• No other changes — one-line root cause, minimal diff.

Root cause

"127.0.0.1:8085".parse().unwrap() is a fixed address. When the OS kernel has not fully released the port from a previous test run, TcpListener::bind fails with EADDRINUSE (os error 98), producing a flaky Server error: ApiError(500, Address already in use). The pattern was already established correctly in tests/server.rs.

Verification

cargo test -p terraphim_server --test default_role_integration_test
# running 2 tests
# test test_default_role_config_structure ... ok
# test test_default_role_ripgrep_integration ... ok
# test result: ok. 2 passed; 0 failed; 0 ignored

cargo clippy -p terraphim_server -- -D warnings  # clean
cargo fmt --all -- --check                        # clean

Refs terraphim/terraphim-ai#2947 (Gitea)