Expose vehicle caravan action boundaries

[sviyh]

Summary

• Route vehicle caravan destinations through vanilla Dialog_FormCaravan.Notify_ChoseRoute while substituting the vehicle-specific exit tile.
• Lift the final vehicle-caravan send action into a named public method.
• Provide stable action boundaries for Multiplayer compatibility without duplicating the surrounding vanilla transaction.

Root cause

Vehicle Framework completed route selection in a custom callback that duplicated part of vanilla's state, estimate, sound, and automatic-supply transaction. Its final send action was also a local function. Multiplayer compatibility therefore had to target lower-level implementation details, and the copied route flow could drift from vanilla behavior.

Approach

The vehicle route planner now returns through vanilla Notify_ChoseRoute. A narrow transpiler replaces only vanilla's exit-tile calculation, selecting CaravanHelper.BestExitTileToGoTo when vehicles are present and retaining the vanilla fallback otherwise. The existing final send body is lifted unchanged into CaravanFormation.TryFormAndSendCaravan.

Test plan

• Vehicle Framework Release build succeeds with no warnings or errors.
• Vanilla Vehicles Expanded rebuilds against the branch assemblies.
• No-vehicle route selection retains vanilla exit selection, ETA, and automatic travel supplies.
• Vehicle route acceptance returns to the caravan dialog with valid estimates and automatic supplies.
• Direct vehicle send starts one forming lord with the selected vehicle, operator, and route intact across 120 ticks.
• Warning/confirmation send starts the same transaction exactly once and remains stable across 120 ticks.
• Manual deployment smoke-tested; the separately observed map-edge warning was isolated against the unmodified upstream base and is not introduced by this diff.