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>

templates/help/index.html.twig

@@ -118,7 +118,7 @@
     <h3><span class="pill pill-green">Step 2 of 2</span> &nbsp; Green screen, single QR code</h3>
     <p>The frame is now on your home WiFi. This QR points at the website where you'll create an account (or sign in) and link the frame to it.</p>
     <ol>
-        <li>Scan the QR. Your browser opens to a setup page on <code>pictureframe.edholm.me</code>.</li>
+        <li>Scan the QR. Your browser opens to a setup page on <code>wevisto.com</code>.</li>
         <li>Create an account or sign in. The frame is linked to whichever account claims it first.</li>
         <li>Upload your first photo. Within a minute or two the frame will pull it down and display it.</li>
     </ol>
@@ -154,7 +154,7 @@
     <p>Frames pull from the server roughly once per configured wake interval (often hourly or every few hours, depending on what you set). If you want the new photo to appear right now, the easiest thing is to <strong>unplug the frame and plug it back in</strong> — a power cycle forces an immediate sync regardless of the schedule.</p>
 
     <h3>The same photo has been showing for a long time</h3>
-    <p>Open <code>pictureframe.edholm.me</code> on your phone, sign in, and check:</p>
+    <p>Open <code>wevisto.com</code> on your phone, sign in, and check:</p>
     <ul>
         <li>The frame is shown as recently active (last sync timestamp).</li>
         <li>Wake times are set to a reasonable schedule — if you set a single daily wake at 9am, that's the only time it will check.</li>