Chore: remove unused imports and suppress unused variable warnings

Removes dead use statements across dispatch, formula, import, model, and
UI modules. Prefixes intentionally unused variables with _ in app.rs,
analyzer.rs, and grid.rs.

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

src/ui/mod.rs

@@ -7,4 +7,3 @@ pub mod tile_bar;
 pub mod import_wizard_ui;
 pub mod help;
 
-pub use app::{App, AppMode};