Improve formatting of mappings html pages

These pages would benefit from some general improvements.

- [ ] Each entry should be one variable per mip table.
- [ ] Some columns should have a search box rather than selection box e.g. expression and comments.
- [ ] Greater width for expression, smaller width for units, status.

Start by locating the mappings HTML pages in the CDDS repository and inspect how entries and table controls are rendered. Compare the current layout with the three requested changes: one variable per MIP table, search boxes for expression and comments, and adjusted column widths. Done means all three formatting improvements are implemented consistently across the mappings pages.

Written by the indexing model from the issue text.