feat: native Qt start panel + kindred:// URL scheme (#167)

Replace QWebEngineView-based start page with a rich native Qt panel.
QWebEngineView (PySide6.QtWebEngineWidgets) is not available on
conda-forge for Qt6, so the start page was always falling back to a
bare offline widget.

Start panel (silo_start.py):
- Database Items list with search from Silo REST API
- Recent Files from FreeCAD preferences
- Real-time Activity Feed via SSE (SiloEventListener)
- Context menu: Open in Create, Open in Browser, Copy Part Number
- 'Open in Browser' button via QDesktopServices
- Catppuccin Mocha dark theme

kindred:// URL scheme:
- Desktop file registers x-scheme-handler/kindred MIME type
- MainWindow::processMessages() dispatches kindred:// URLs to Python
- handle_kindred_url() in silo_commands.py opens items by part number
- InitGui.py handles kindred:// URLs on cold start via QTimer

Closes #167

resources/kindred-create.desktop

@@ -2,12 +2,12 @@
 Name=Kindred Create
 GenericName=CAD Application
 Comment=Parametric 3D CAD modeler based on FreeCAD
-Exec=kindred-create %F
+Exec=kindred-create %U
 Icon=kindred-create
 Terminal=false
 Type=Application
 Categories=Graphics;Science;Engineering;
-MimeType=application/x-extension-fcstd;
+MimeType=application/x-extension-fcstd;x-scheme-handler/kindred;
 Keywords=CAD;3D;modeling;engineering;design;parametric;
 StartupNotify=true
 StartupWMClass=KindredCreate

src/Gui/MainWindow.cpp

@@ -1700,10 +1700,27 @@ void MainWindow::processMessages(const QList<QString>& msg)
     try {
         WaitCursor wc;
         std::list<std::string> files;
-        QString action = QStringLiteral("OpenFile:");
+        QString openFileAction = QStringLiteral("OpenFile:");
+        QString kindredScheme = QStringLiteral("kindred://");
         for (const auto& it : msg) {
-            if (it.startsWith(action)) {
-                files.emplace_back(it.mid(action.size()).toStdString());
+            if (it.startsWith(openFileAction)) {
+                QString payload = it.mid(openFileAction.size());
+                if (payload.startsWith(kindredScheme)) {
+                    // Dispatch kindred:// URLs to the Python handler
+                    std::string urlStr = payload.toStdString();
+                    std::string script = "try:\n"
+                                         "    from silo_commands import handle_kindred_url\n"
+                                         "    handle_kindred_url('"
+                        + urlStr
+                        + "')\n"
+                          "except Exception as e:\n"
+                          "    FreeCAD.Console.PrintError("
+                          "'Kindred URL handler error: ' + str(e) + '\\n')\n";
+                    Base::Interpreter().runString(script.c_str());
+                }
+                else {
+                    files.emplace_back(payload.toStdString());
+                }
             }
         }
         files = App::Application::processFiles(files);