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/theme.rs

@@ -3,9 +3,9 @@
 //! Zig reads the resources dir from global state; here it is passed
 //! explicitly (`resources_dir`, the value of `ResourcesDir.app()`).
 
+use std::{fs::File, path::Path};
+
 use crate::diagnostics::{Diagnostic, DiagnosticList};
-use std::fs::File;
-use std::path::Path;
 
 /// Location of possible themes. The order of this enum matters because it
 /// defines the priority of theme search (from top to bottom).