refactor!: unify records and pivot mode cell handling

Refactor records mode to use synthetic CellKeys (_Index, _Dim) for all columns,
allowing uniform handling of display values and edits across both pivot and
records modes.

- Introduce `synthetic_record_info` to extract metadata from synthetic keys.
- Update `GridLayout::cell_key` to return synthetic keys in records mode.
- Add `GridLayout::resolve_display` to handle value resolution for synthetic
  keys.
- Replace `records_col` and `records_value` in `CmdContext` with a unified
  `display_value`.
- Update `EditOrDrill` and `AddRecordRow` to use synthetic key detection.
- Refactor `CommitCellEdit` to use a shared `commit_cell_value` helper.

BREAKING CHANGE: CmdContext fields `records_col` and `records_value` are replaced by
`display_value` .
Co-Authored-By: fiddlerwoaroof/git-smart-commit (unsloth/gemma-4-31B-it-GGUF:UD-Q5_K_XL)

src/view/mod.rs

@@ -3,5 +3,5 @@ pub mod layout;
 pub mod types;
 
 pub use axis::Axis;
-pub use layout::{AxisEntry, GridLayout};
+pub use layout::{synthetic_record_info, AxisEntry, GridLayout};
 pub use types::View;