fix(toolbar): add workbench-level fallback contexts (#230)

PartDesign, Sketcher, and Assembly toolbars use
DefaultVisibility::Unavailable and rely on EditingContextResolver to
show them. When switching to these workbenches without a specific editing
state (e.g. PartDesign with no Body activated), no context matches and
all workbench toolbars stay hidden.

Add workbench-level fallback contexts at priority 20 that match when the
workbench is active regardless of editing state:
- partdesign.workbench: shows Helper Features + Sketcher toolbars
- sketcher.workbench: shows Sketcher + Sketcher Tools
- assembly.workbench: shows Assembly toolbar

These fill the gap between object-specific contexts (priority 30+) and
the empty_document fallback (priority 10).

src/Gui/EditingContext.cpp

@@ -36,6 +36,7 @@
 #include "ToolBarManager.h"
 #include "ViewProvider.h"
 #include "ViewProviderDocumentObject.h"
+#include "WorkbenchManager.h"
 
 using namespace Gui;
 
@@ -330,6 +331,49 @@ void EditingContextResolver::registerBuiltinContexts()
         },
     });
 
+    // --- Workbench-level fallbacks (priority 20) ---
+    // Show basic workbench toolbars when the workbench is active but no
+    // specific editing context matches (e.g. no Body selected in PartDesign).
+
+    registerContext({
+        /*.id =*/QStringLiteral("partdesign.workbench"),
+        /*.labelTemplate =*/QStringLiteral("Part Design"),
+        /*.color =*/QLatin1String(CatppuccinMocha::Mauve),
+        /*.toolbars =*/
+        {QStringLiteral("Part Design Helper Features"), QStringLiteral("Sketcher")},
+        /*.priority =*/20,
+        /*.match =*/
+        []() {
+            return WorkbenchManager::instance()->activeName() == "PartDesignWorkbench";
+        },
+    });
+
+    registerContext({
+        /*.id =*/QStringLiteral("sketcher.workbench"),
+        /*.labelTemplate =*/QStringLiteral("Sketcher"),
+        /*.color =*/QLatin1String(CatppuccinMocha::Green),
+        /*.toolbars =*/
+        {QStringLiteral("Sketcher"), QStringLiteral("Sketcher Tools")},
+        /*.priority =*/20,
+        /*.match =*/
+        []() {
+            return WorkbenchManager::instance()->activeName() == "SketcherWorkbench";
+        },
+    });
+
+    registerContext({
+        /*.id =*/QStringLiteral("assembly.workbench"),
+        /*.labelTemplate =*/QStringLiteral("Assembly"),
+        /*.color =*/QLatin1String(CatppuccinMocha::Blue),
+        /*.toolbars =*/
+        {QStringLiteral("Assembly")},
+        /*.priority =*/20,
+        /*.match =*/
+        []() {
+            return WorkbenchManager::instance()->activeName() == "AssemblyWorkbench";
+        },
+    });
+
     // --- Empty document ---
     registerContext({
         /*.id =*/QStringLiteral("empty_document"),