fe: default check path to project root or CWD when omitted

[quantumshiro]

i fixed #1122

Changes

• Add Clap default for Check’s path:
  • #[arg(default_value_t = default_project_path())]
• Add default_project_path() helper using driver::files::find_project_root().unwrap_or(Utf8PathBuf::from(".")).
• Only touches crates/fe/src/main.rs. No other logic or behavior changed.

Examples

• fe check → checks current project
• fe check ./contracts → checks given directory
• fe check ./example.fe → checks given single file

Testing

• Built successfully with cargo check -p fe.
• Manual runs:
  • Repo root (non-project): shows missing fe.toml/src errors (expected).
  • Inside fixture project (crates/fe/tests/fixtures/cli_output/ingots/basic): success.
  • Inside src/ under the project: success (root auto-detected).

[sbillig]

👍