Fire Behaviour Calculator: Header tooltips are getting cut off

**Describe the Bug**
Header tooltips are still getting cut off on the left side when you scroll across the table and some header cells scroll behind sticky cells. Discovered in #1492 but pulled into a separate ticket here.

**Expected Behaviour**
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**Actual Behaviour**
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** Steps To Reproduce**
Steps to reproduce the behaviour:
1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

**Screenshots**
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**Desktop (please complete the following information):**
- OS: [e.g. iOS]
- Browser [e.g. chrome, safari]
- Version [e.g. 22]

**Additional context**
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Start at the Fire Behaviour Calculator UI and reproduce the issue by scrolling across the table headers. Inspect the tooltip and sticky-header behavior at the left edge; done means header tooltips remain fully visible and header cells do not scroll behind sticky cells.

Written by the indexing model from the issue text.