fix(gui): resolve PartDesign toolbars and breadcrumb when editing body inside assembly

When double-clicking a PartDesign Body inside an Assembly, the editing
context resolver failed to show PartDesign toolbars or a proper
breadcrumb. Three root causes:

1. Priority preemption: assembly.edit (priority 90) always matched
   because the Assembly VP remained in edit mode, blocking all
   PartDesign contexts (priorities 30-40).

2. Wrong active-object key: PartDesign matchers only queried the
   "part" active object, but ViewProviderBody::toggleActiveBody()
   sets "part" to the containing App::Part (which is the Assembly
   itself). The Body is set under "pdbody", which was never queried.

3. Missing refresh trigger: ActiveObjectList::setObject() fires
   Document::signalActivatedViewProvider, but EditingContextResolver
   had no connection to it, so setActiveObject("pdbody", body) never
   triggered a context re-resolve.

Changes:
- Forward signalActivatedViewProvider from Gui::Document to
  Gui::Application (same pattern as signalInEdit/signalResetEdit)
- Connect EditingContextResolver to the new application-level signal
- Add getActivePdBodyObject() helper querying the "pdbody" key
- Add partdesign.in_assembly context (priority 95) that matches when
  a Body is active pdbody while an Assembly is in edit
- Update partdesign.body and partdesign.feature matchers to check
  pdbody before falling back to the part key
- Add Assembly > Body breadcrumb with Blue > Mauve coloring
- Update label resolution to prefer pdbody name

src/Gui/Application.cpp

@@ -1046,6 +1046,9 @@ void Application::slotNewDocument(const App::Document& Doc, bool isMainDoc)
     );
     pDoc->signalInEdit.connect(std::bind(&Gui::Application::slotInEdit, this, sp::_1));
     pDoc->signalResetEdit.connect(std::bind(&Gui::Application::slotResetEdit, this, sp::_1));
+    pDoc->signalActivatedViewProvider.connect(
+        std::bind(&Gui::Application::slotActivatedViewProvider, this, sp::_1, sp::_2)
+    );
     // NOLINTEND
 
     signalNewDocument(*pDoc, isMainDoc);
@@ -1352,6 +1355,12 @@ void Application::slotResetEdit(const Gui::ViewProviderDocumentObject& vp)
     this->signalResetEdit(vp);
 }
 
+void Application::slotActivatedViewProvider(
+    const Gui::ViewProviderDocumentObject* vp, const char* name)
+{
+    this->signalActivatedViewProvider(vp, name);
+}
+
 void Application::onLastWindowClosed(Gui::Document* pcDoc)
 {
     try {