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-config/src/file_load.rs

@@ -2,9 +2,10 @@
 //!
 //! macOS Application Support paths are not supported (Linux only).
 
-use ghostty_os::xdg;
 use std::fs::File;
 
+use ghostty_os::xdg;
+
 /// Default path for the XDG home configuration file.
 pub fn default_xdg_path() -> Result<String, xdg::Error> {
     xdg::config(&xdg::Options {