Release v0.5.0

- Auto-create default `config.toml` on first run (no manual `init` step needed)
- `ait config validate` — checks TOML syntax, glob patterns, and API key env var
- `ait config path` — prints config file path (composable: `subl $(ait config path)`)
- `ait config edit` — opens config in `$EDITOR` (fallback: `vi`)
- Well-commented default config template with all safety rules and provider settings
- `DEFAULT_CONFIG_TEMPLATE` constant in `config.rs` for reuse
- 4 new unit tests (default template parsing, glob validation, invalid pattern detection)

- `ConfigError` variants renamed from `ReadError`/`WriteError`/`ParseError` to `Read`/`Write`/`Parse` (clippy `enum_variant_names`)
- CLI now uses `clap` subcommands (`#[derive(Subcommand)]`) alongside trailing var args
- `--debug` flag is now global (works with subcommands too)