SFMS Insights: Date/Data Layer in URL

**Describe the task**
The date (and data layer?) should be in the URL to enable link sharing & bookmarking.

**Acceptance Criteria**
- [ ] first
- [ ] second
- [ ] third

**Additional context**
- Add any other context about the task here.
- Or here

Start by locating the SFMS Insights view and its routing or URL state handling. Determine how the selected date and data layer are currently stored, then verify that sharing or bookmarking the URL restores both selections. The issue's acceptance criteria are placeholders, so confirm the intended behavior before implementation.

Written by the indexing model from the issue text.