docs(research): third street run; lane connections and the crossing tool

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/research/vehicle-probe.md

@@ -105,3 +105,5 @@ The human confirmed in game what the log showed: rebuilding the segment under a
   - Visually the lane change is abrupt (human: "the lanes need a smoother transition"): the switch happens at the node, which has almost zero length on a straight, and the jump is about 5–6 m sideways.
   - Next ideas: a lower speed limit on the passing lane (prefer the normal lane unless it's blocked), a smaller offset or transition segments for a smoother change.
 - Third run setup: passing lanes at 20 m/s (normal lanes 22.22 m/s), everything else unchanged. Question: does a lower limit keep vehicles in the normal lane and send them to the passing lane only when the normal lane is blocked?
+- Third run (20 m/s passing lanes): **no change.** Slow buses still sat in the left passing lane (29849 and 29851: 29/29 samples in lane 3); fast 29251 split 8/11. The engine doesn't pick lanes by speed limit (the slow buses top out at 16.67 < 20 anyway). Observed pattern: a vehicle gets a lane when it enters the stretch and keeps it; it doesn't move over when blocked; passes happen only when fast and slow happen to be in different lanes.
+- Lane connections are editable: `BaseNodeConfig.laneConnections` (`LaneConnection{segment0, lane0, segment1, lane1, withRoad, withTram}`, lanes zero-based left-to-right seen from the node) plus `userModifiedLaneConnections`, scriptable via `SimpleStreetProposal.nodeConfigsToAdd`. The game also has a native **crossing tool** ("allows to change the road and tram lanes at crossings", `UI::LaneModifier` in the executable). Next test (option a, by hand): at the stretch's entry junction, connect the normal road only to the right lane, to see whether entry control works and whether a blocked fast bus moves left inside the stretch.