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/import/mod.rs

@@ -1,5 +1,3 @@
 pub mod wizard;
 pub mod analyzer;
 
-pub use wizard::{ImportWizard, ImportPipeline, WizardStep};
-pub use analyzer::{FieldKind, FieldProposal, analyze_records};