Editor checkpoint: turnout domain service, web->editor rename, Id-1 templates

Checkpoint of the editor branch so work isn't carried loose across a branch
switch. Builds.

- maj0sted turnout geometry moved into the domain: domain::lay_turnout lays the
  diverging path (pre-blade lead, blade at beta, arc of alfa-beta, frog rail) and
  solve_junction is a thin adapter onto it.
- the maj0sted web/ tree renamed to editor/ (namespace and paths) - there is no
  WASM here, it's plain native C++ the editor calls.
- click places the switch at its start (początek rozjazdu); the branch's leaving
  straight is locked tangent to the frog; switches can be slid along the through
  track and flipped L/P.
- Polish turnout templates carry catalogue length (Id-1-consistent lengths), plus
  blade-angle and pre-blade fields (left 0 until the catalogue figures are in).
- TURNOUT_SPEC.md: the Bezier-based runtime/model contract.
- also folds in other pending branch changes (scenery, tests) to leave a clean tree.

simulation/simulationstateserializer.cpp

@@ -40,6 +40,10 @@ state_serializer::deserialize_begin( std::string const &Scenariofile ) {
     // its sections, which those chunks referenced) is destroyed below
     EditorTerrain.reset();
 
+    // groups hold raw pointers into the region; wipe them before the region goes away so a reload
+    // cannot walk dangling nodes in update_map() / erase()
+    scene::Groups.clear();
+
     // TODO: move initialization to separate routine so we can reuse it
     SafeDelete( Region );
     Region = new scene::basic_region();