feat: add streaming(loading) for smtp settings page navigation (#264)

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

apps/web/src/app/(dashboard)/dev-settings/smtp/loading.tsx

@@ -0,0 +1,40 @@
+import { Card, CardContent, CardDescription, CardHeader, CardTitle } from "@usesend/ui/src/card";
+  export default function Loading() {
+    return (
+      <Card className="mt-9 max-w-xl">
+        <CardHeader>
+          <CardTitle>SMTP</CardTitle>
+          <CardDescription>
+            Send emails using SMTP instead of the REST API. See documentation for
+            more information.
+          </CardDescription>
+        </CardHeader>
+        <CardContent>
+          <div className="space-y-6">
+            <div>
+              <strong>Host:</strong>
+              <div className="ml-1 border bg-primary/10 rounded-lg mt-1 p-2 w-full h-10 animate-pulse" />
+            </div>
+            <div>
+              <label>Port:</label>
+              <div className="ml-1 rounded-lg mt-1 p-2 w-full bg-primary/10 h-10 animate-pulse" />
+              <p className="ml-1 mt-1 text-zinc-500 text-sm">
+                For encrypted/TLS connections use{" "}
+                <strong className="font-mono">2465</strong>,{" "}
+                <strong className="font-mono">587</strong> or{" "}
+                <strong className="font-mono">2587</strong>
+              </p>
+            </div>
+            <div>
+              <label>User:</label>
+              <div className="ml-1 rounded-lg mt-1 p-2 w-full bg-primary/10 h-10 animate-pulse" />
+            </div>
+            <div>
+              <label>Password:</label>
+              <div className="ml-1 rounded-lg mt-1 p-2 w-full bg-primary/10 h-10 animate-pulse" />
+            </div>
+          </div>
+        </CardContent>
+      </Card>
+    );
+  }