Unifies cell text retrieval and formatting across pivot and records modes.
Introduces `GridLayout::display_text` to centralize how cell content is
resolved, reducing duplication in `GridWidget` and `export_csv`.
Moves formatting logic from `src/ui/grid.rs` to a new dedicated `src/format.rs`
module to improve reusability.
Co-Authored-By: fiddlerwoaroof/git-smart-commit (unsloth/gemma-4-31B-it-GGUF:UD-Q5_K_XL)
