UX: WebView native-feel + Context-Menu Redesign + Startup-Fix

- Disable text selection (CSS user-select:none) + block browser
  context menu (contextmenu preventDefault) in all panels
- ContextMenu: pill items, accent hover, entrance animation,
  optional title header — controlled via single ContextMenu.css
- EbenenManager + GeschossManager: show layer name as menu title
- startup.py: skip splash on Cmd+N when plugin already loaded
- startup.py: hook NewDocument so display-modes apply to new docs

rhino/startup.py

@@ -23,11 +23,13 @@ if _HERE not in sys.path:
 # Nutzer waehrend Python-Imports + Panel-Registrierung nicht in eine schwarze
 # Rhino-Oberflaeche schaut. Skipt automatisch wenn Launcher seinen eigenen
 # Splash zeigt (Owner-Marker-Check).
-try:
-    import _startup_splash as _splash_first
-    _splash_first.show()
-except Exception as _ex_splash:
-    print("[STARTUP] splash early:", _ex_splash)
+# Skipt auch wenn Plugin bereits in dieser Session geladen ist (z.B. Cmd+N).
+if not sc.sticky.get("_dossier_startup_scheduled"):
+    try:
+        import _startup_splash as _splash_first
+        _splash_first.show()
+    except Exception as _ex_splash:
+        print("[STARTUP] splash early:", _ex_splash)
 
 # DIAGNOSE — welcher Python-Engine laeuft hier wirklich? Einmalig beim Start.
 print("[STARTUP] Python: {}".format(sys.version))
@@ -299,6 +301,10 @@ def _load_all(sender, e):
         Rhino.RhinoDoc.EndOpenDocument += _on_doc_opened
     except Exception as ex:
         print("[STARTUP] EndOpenDocument-Hook:", ex)
+    try:
+        Rhino.RhinoDoc.NewDocument += _on_doc_opened
+    except Exception as ex:
+        print("[STARTUP] NewDocument-Hook:", ex)
     # Projekt-Config bestimmt, welche Module geladen werden. Ohne Config
     # (kein Launcher benutzt, oder Datei nicht da) laedt der Host alles.
     config = _read_project_config()