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/lib/TitleBar.svelte

@@ -3,6 +3,7 @@
   import { getVersion } from "@tauri-apps/api/app";
   import { getCurrentWindow } from "@tauri-apps/api/window";
   import { CloudDownload, Download, FolderOpen, GitBranch, GitCompare, LoaderCircle, Minus, RefreshCw, Search, Settings, Upload, X } from "@lucide/svelte";
+  import iconUrl from "../../src-tauri/icons/icon.png";
 
   export let branch: string = "";
   export let ahead: number = 0;
@@ -44,24 +45,9 @@
 <header class="titlebar" data-tauri-drag-region>
   <!-- Brand -->
   <div class="titlebar-brand" data-tauri-drag-region>
-    <svg
-      width="15"
-      height="15"
-      viewBox="0 0 24 24"
-      fill="none"
-      stroke="currentColor"
-      stroke-width="2"
-      stroke-linecap="round"
-      stroke-linejoin="round"
-      aria-hidden="true"
-      data-tauri-drag-region
-    >
-      <circle cx="12" cy="18" r="3" />
-      <circle cx="6" cy="6" r="3" />
-      <circle cx="18" cy="6" r="3" />
-      <path d="M18 9v1a2 2 0 0 1-2 2H8a2 2 0 0 1-2-2V9" />
-      <line x1="12" y1="12" x2="12" y2="15" />
-    </svg>
+    <span class="titlebar-brand-icon" data-tauri-drag-region>
+      <img src={iconUrl} alt="" data-tauri-drag-region />
+    </span>
     <span data-tauri-drag-region>GitLite</span>
     {#if appVersion}
       <span class="tb-version" data-tauri-drag-region title="Version {appVersion}">v{appVersion}</span>