fix coming soon page: crash, logo centering, admin login link

Add AnalyticsHook to the coming_soon live session — the shop layout
fires an analytics:screen JS event but the session had no handler,
crashing the page on connect.

Centre the logo image (display:block from CSS reset needs
margin-inline:auto). Add a subtle "Admin" link at the bottom using
flex flow rather than fixed/absolute positioning so it works in
iframes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

assets/css/shop/components.css

@@ -2766,12 +2766,16 @@
 
   .coming-soon {
     display: flex;
+    flex-direction: column;
     align-items: center;
-    justify-content: center;
     min-height: 100vh;
     min-height: 100dvh;
-    padding-inline: 1.5rem;
+    padding: 1.5rem;
     text-align: center;
+
+    & > :first-child {
+      margin-block: auto;
+    }
   }
 
   .coming-soon-logo {
@@ -2780,6 +2784,7 @@
     & img {
       max-height: 4rem;
       max-width: 12rem;
+      margin-inline: auto;
       object-fit: contain;
     }
   }
@@ -2798,6 +2803,16 @@
     font-size: 1.125rem;
     color: var(--t-text-secondary);
   }
+
+  .coming-soon-admin-link {
+    font-size: 0.75rem;
+    color: var(--t-text-tertiary);
+    text-decoration: none;
+
+    &:hover {
+      color: var(--t-text-secondary);
+    }
+  }
 }
 
 @layer components {