fix: align cwd flag names

[nijanthanvijayakumar]

Summary

• use --cwd as the canonical working-directory flag
• keep --cd as a compatibility alias
• clean up two compile warnings hit while testing

Tests

• cargo test -p cortex-cli cwd
• cargo test -p cortex-tui external_editor

Docker smoke

Command:

docker run --rm -v "$PWD:/work" -v cortex-cargo-registry:/usr/local/cargo/registry -v cortex-target:/tmp/cortex-target -w /work -e CARGO_TARGET_DIR=/tmp/cortex-target rust:latest bash -lc 'apt-get update >/dev/null && apt-get install -y --no-install-recommends libasound2-dev >/dev/null; export PATH=/usr/local/cargo/bin:$PATH; printf "toolchain: "; rustc --version; printf "root: "; cargo run -p cortex-cli -- --help | grep -E -- "-C, --cwd|--cd"; printf "acp: "; cargo run -p cortex-cli -- acp --help | grep -E -- "-C, --cwd|--cd"; printf "shell: "; cargo run -p cortex-cli -- shell --help | grep -E -- "-C, --cwd|--cd"'

Output:

toolchain: rustc 1.95.0 (59807616e 2026-04-14)
root:   -C, --cwd <DIR>
acp:   -C, --cwd <DIR>
shell:   -C, --cwd <CWD>