feat(splashscreen): implement a splash screen for application startup

This commit introduces a splash screen that enhances the user experience during application startup. It includes a new HTML file for the splash screen layout and a corresponding icon. The main application logic has been updated to close the splash screen once the main application is ready.

- Added a splash screen HTML and icon for improved visual feedback
- Updated main application logic to manage splash screen visibility
- Enhanced title bar branding with an image instead of SVG

src-tauri/tauri.conf.json

@@ -18,8 +18,21 @@
         "height": 800,
         "minWidth": 900,
         "minHeight": 600,
+        "visible": false,
         "decorations": false,
         "shadow": true
+      },
+      {
+        "label": "splashscreen",
+        "url": "splashscreen.html",
+        "title": "GitLite",
+        "width": 460,
+        "height": 420,
+        "resizable": false,
+        "decorations": false,
+        "center": true,
+        "skipTaskbar": true,
+        "shadow": true
       }
     ],
     "security": {