feat(ui): add dynamic column widths for records mode

Implement dynamic column widths for the grid widget when in records mode.

In records mode, each column width is computed based on the widest
content (pending edit, record value, or header label), with a minimum
of 6 characters and maximum of 32. Pivot mode continues to use fixed
10-character column widths.

The rendering code has been updated to use the computed column widths
and x-offsets for all grid elements: headers, data cells, and totals.
Note that the total row is now only displayed in pivot mode, as it
is not meaningful in records mode.

Co-Authored-By: fiddlerwoaroof/git-smart-commit (unsloth/Qwen3.5-35B-A3B-GGUF:Q5_K_M)

src/command/cmd.rs

@@ -2647,6 +2647,7 @@ mod tests {
             view_back_stack: Vec::new(),
             view_forward_stack: Vec::new(),
             records_col: None,
+            records_value: None,
             cell_key: layout.cell_key(sr, sc),
             row_count: layout.row_count(),
             col_count: layout.col_count(),