Resolves the 3 remaining gaps in docs/rewrite/notes/review-rv11-codex.md
(final-Z14.md):
- ghostty-bench validates every occurrence of enum options in order
(Args::take_enum; empty value resets) like cli/args.zig, so
`--mode=bad --mode=noop` fails as in Zig.
- Theme paths with an interior NUL open the prefix like Zig's C-string
path handling (verified against /usr/bin/ghostty).
- Filesystem diagnostics print Zig's error names (error.FileNotFound,
NotDir, AccessDenied, IsDir, NameTooLong, SymLinkLoop, ...) via a
shared ghostty_os::zig_error mapping used by theme/path/config-file/
file_load/edit-config/list-themes; messages match the oracle.
Test Plan:
- cargo test --workspace --no-fail-fast
- just check-macos (both), just check-windows, just check-wasm
