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.

scene/scenenodegroups.cpp

@@ -53,6 +53,16 @@ node_groups::close()
     return handle();
 }
 
+void
+node_groups::clear()
+{
+    // nodes/events are owned by the region (or already gone with it); do not dereference them
+    m_groupmap.clear();
+    while( false == m_activegroup.empty() ) {
+        m_activegroup.pop();
+    }
+}
+
 bool node_groups::assign_cross_switch(map::track_switch& sw, std::string &sw_name, std::string const &id, size_t idx)
 {
     sw.action[idx] = simulation::Events.FindEvent(sw_name + ":" + id);