style: apply cargo fmt formatting to existing codebase

Run `cargo fmt` across all Rust source files to enforce consistent
formatting (import ordering, line wrapping, match arm braces).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/application/dtos/folder_dto.rs

@@ -54,7 +54,6 @@ pub struct FolderDto {
     pub is_root: bool,
 
     // ── Pre-computed display fields ──
-
     /// FontAwesome icon CSS class (always "fas fa-folder")
     pub icon_class: String,