Mark as main road along snapped route

- [ ] While drawing a route, other layers are still interactive, like "Click to delete a turn restriction"
- [x] Should we allow erasing main roads along a route?
- [ ] Should we have an explicit 'Finish' button or other controls to confirm a route? Or style the last waypoint? https://github.com/a-b-street/ltn/pull/382#pullrequestreview-2922024241
- [ ] #295 - Can we use similar controls to change the one-way direction along an entire long bit of road? (Not sure how to determine that direction -- toggle between two-ways, all one-way in one direction, all one-way in the other)
- [x] Remove `reclassifications_in_progress`, an old field that breaks binary compatibility. (And more rigorously `serde(skip)` things like this)