style: apply nightly rustfmt import grouping across the workspace

rustfmt.toml sets group_imports, imports_granularity and imports_layout,
which are nightly-only; agents formatted with stable rustfmt, which
ignored them. This is a formatting-only pass with `cargo +nightly fmt`.

Test Plan:
- cargo clippy --workspace --all-targets -- -D warnings
- cargo test --workspace

crates/ghostty-os/src/xdg.rs

@@ -3,8 +3,7 @@
 
 use std::ffi::CStr;
 
-use crate::env::getenv_not_empty;
-use crate::{homedir, path_join};
+use crate::{env::getenv_not_empty, homedir, path_join};
 
 #[derive(Debug, Clone, Default)]
 pub struct Options<'a> {