feat(brand): switch user-facing copy + Mercure topic prefix to wevisto.com

Mercure topic identifiers updated in lockstep across PHP publisher + TS
subscriber (and their tests). Help-page setup instructions now point to
wevisto.com. Traefik already serves both hosts; this aligns the in-app
references with the public brand.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/Unit/Service/MercurePublisherTest.php

@@ -35,7 +35,7 @@ class MercurePublisherTest extends TestCase
 
         $this->assertNotNull($captured);
         $this->assertSame(
-            ['https://pictureframe.edholm.me/devices/42'],
+            ['https://wevisto.com/devices/42'],
             $captured->getTopics(),
         );
         $this->assertSame('{"id":42,"name":"Living Room"}', $captured->getData());