feat: point the feedback email footer at the Dev Center

The footer told developers to turn feedback off via a puter.apps.update
one-liner, but the toggle lives in the Dev Center app settings — and
Dev Center is where apps get feedback enabled by default in the first
place. Reword it to 'manage it in the Dev Center' with a link built
from config.origin (like app_link) so it holds on self-hosted
deployments.

src/backend/clients/email/templates.ts

@@ -88,9 +88,9 @@ The Puter Team
 <blockquote>{{{nl2br message}}}</blockquote>
 {{#if sender_email}}<p>Just reply to this email to respond to them directly.</p>{{/if}}
 <p>
-You're receiving this because user feedback is enabled for your app. To stop
-receiving these emails, turn off feedback for the app (e.g.
-<code>puter.apps.update({ name: '{{app_name}}', feedbackEnabled: false })</code>).
+You're receiving this because feedback is enabled for
+<a href="{{app_link}}">{{app_title}}</a> — manage it in the
+<a href="{{dev_center_link}}">Dev Center</a> under your app's settings.
 </p>
 <p>Best,<br />
 The Puter Team

src/backend/services/feedback/AppFeedbackService.ts

@@ -343,6 +343,10 @@ export class AppFeedbackService extends PuterService {
                     ),
                     app_name: String(app.name),
                     app_link: `${this.config.origin}/app/${encodeURIComponent(String(app.name))}`,
+                    // The footer's "manage it" pointer — built from
+                    // config.origin like app_link so it holds on self-hosted
+                    // deployments.
+                    dev_center_link: `${this.config.origin}/app/dev-center`,
                     message,
                 },
                 senderEmail ? { replyTo: senderEmail } : {},