Fire Behaviour Calculator (old) Table: Select state

**As a** *FBAN* **I want** *clear interface cues* **So That** *it is very apparent to me when I have selected 1+ rows, even when I scroll*

**Additional Context**
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- enter text here

**Acceptance Criteria**
- [ ] Given I am using FireBAT, When 1+ row(s) are selected, The row(s) have a select state (background colour) that you can see even if you have scrolled horizontally and the checkbox is not visible (always clear which rows I am performing actions on)

**Definition of Done**
- [ ] Ready to Demo in Sprint Review
- [ ] Does what I have made have appropriate test coverage?
- [ ] Documentation and/or scientific documentation exists and can be found
- [ ] Peer Reviewed by 2 people on the team
- [ ] Manual testing of all PRs in Dev and Prod
- [ ] Merged

Locate the old Fire Behaviour Calculator table in the repository and inspect how row selection is rendered and tracked. Reproduce selecting one or more rows, then scroll horizontally to confirm the selected rows remain visually identifiable when their checkboxes are off-screen. Done means the selection state is clear and the relevant behavior has appropriate test coverage.

Written by the indexing model from the issue text.