fix: reposition flash on mobile.

[teesloane]

Describe your changes

closes #346

I was originally overthinking this - adding a new flash library is fairly involved. Why not just move the flash down to within thumbs reach on mobile (and get it out of the way of menu).

If we need to explore future flash libraries, Flashy looks good, and so does LiveToast. Both involve having to setup JS hooks.

Screenshot

https://github.com/bikebrigade/dispatch/assets/12987958/3a354b4c-c102-4d91-ae2c-72bde00e593f

Checklist before requesting a review

• [x] I have performed a self-review of my code
• [n/a] If it is a core feature, I have added tests.
• [n/a] Are there other PRs or Issues that I should link to here?
• [n/a] Will this be part of a product update? If yes, please write one phrase about this update in the description above.