Cleanup code_mode tool descriptions (#14480)

Move to separate files and clarify a bit.

codex-rs/Cargo.lock

@@ -1439,6 +1439,7 @@ dependencies = [
  "codex-utils-cargo-bin",
  "codex-utils-cli",
  "codex-utils-json-to-toml",
+ "codex-utils-pty",
  "core_test_support",
  "futures",
  "opentelemetry",
@@ -2438,7 +2439,6 @@ dependencies = [
  "anyhow",
  "chrono",
  "clap",
- "codex-otel",
  "codex-protocol",
  "dirs",
  "log",