feat: Add GitHub link button to Navbar for easy access to repository

Author: nannany

ui/src/components/Navbar.tsx

@@ -41,9 +41,33 @@ const Navbar = () => {
   return (
     <nav className="border-b bg-background px-4 py-3">
       <div className="flex items-center justify-between">
-        <Link to="/" className="text-xl font-bold">
-          タスクマネージャー
-        </Link>
+        <div className="flex items-center gap-4">
+          <Link to="/" className="text-xl font-bold">
+            タスクマネージャー
+          </Link>
+          <Button
+            asChild
+            variant="ghost"
+            size="sm"
+            className="flex items-center gap-1 text-muted-foreground hover:text-foreground"
+          >
+            <a
+              href="https://github.com/nannany/tryjunie"
+              target="_blank"
+              rel="noopener noreferrer"
+            >
+              <svg
+                className="h-4 w-4"
+                fill="currentColor"
+                viewBox="0 0 24 24"
+                xmlns="http://www.w3.org/2000/svg"
+              >
+                <path d="M12 0c-6.626 0-12 5.373-12 12 0 5.302 3.438 9.8 8.207 11.387.599.111.793-.261.793-.577v-2.234c-3.338.726-4.033-1.416-4.033-1.416-.546-1.387-1.333-1.756-1.333-1.756-1.089-.745.083-.729.083-.729 1.205.084 1.839 1.237 1.839 1.237 1.07 1.834 2.807 1.304 3.492.997.107-.775.418-1.305.762-1.604-2.665-.305-5.467-1.334-5.467-5.931 0-1.311.469-2.381 1.236-3.221-.124-.303-.535-1.524.117-3.176 0 0 1.008-.322 3.301 1.23.957-.266 1.983-.399 3.003-.404 1.02.005 2.047.138 3.006.404 2.291-1.552 3.297-1.23 3.297-1.23.653 1.653.242 2.874.118 3.176.77.84 1.235 1.911 1.235 3.221 0 4.609-2.807 5.624-5.479 5.921.43.372.823 1.102.823 2.222v3.293c0 .319.192.694.801.576 4.765-1.589 8.199-6.086 8.199-11.386 0-6.627-5.373-12-12-12z" />
+              </svg>
+              GitHub
+            </a>
+          </Button>
+        </div>
         <div className="flex items-center gap-4">
           {isLoading ? (
             // ローディング中は何も表示しない、またはローディングインジケーターを表示