Refresh ride camera scope when vehicle attachment changes

[mayor-modder]

This follows up by refreshing the camera's ride context whenever its temporary vehicle attachment changes. That fixes the rail-level ride camera and avoids asking localization for unresolved internal rail-track labels, which could trigger repeated errors.

Summary

• Refresh vehicle/citizen scope when the resolved camera attachment target changes.
• Recalculate ride offsets after a followed citizen attaches to a vehicle, so vehicle rides use the vehicle camera offset instead of the pedestrian offset.
• Avoid rail-track label lookups in the transit strip map and ignore unresolved asset labels.

Stack

Stacked on: Cgameworld#9 (codex/follow-subject-through-vehicles).

Validation

• dotnet test Tests/FollowTargetStateTests.csproj --no-restore (5 passed)
• dotnet build FirstPersonCameraContinued.csproj /p:ModPublisherCommand=Update /m:1 /nodeReuse:false /p:UseSharedCompilation=false (0 errors; existing nullable warnings remain)
• Local gameplay retesting followed a citizen through subway boarding and disembarking, and the subway ride used the vehicle-height camera instead of rail-level positioning.

Notes

This PR is intentionally opened in the fork because the stack base branch is not available in the upstream repository. After the base PR lands upstream, this branch can be retargeted or rebased for an upstream PR with the same focused diff.