contact messages: hide the mail server field until the backend lands

The setting plumbing (Data field, /_api/settings, editor refs) stays; the
input is commented out of the messaging grid, which goes back to three
columns. Also: the admin watch skips unread:false thread pushes, so a
read-marking echo for a thread beyond the watch's baseline cap can no
longer fire a spurious new-message notification.

frontend/src/SiteEditor.vue

@@ -833,6 +833,10 @@ onUnmounted(() => {
             @input="debounce('contact-email', () => saveSettings())"
           />
         </label>
+        <!-- Mail server (SMTP notification backend): plumbing in place
+             (contactMailserver ref, settings load/save, Data field) but
+             the sending is not implemented yet — the field stays hidden
+             until then. Re-adds a fourth column to .msg-grid.
         <label class="field">
           <span class="field-label">mail server</span>
           <input
@@ -849,6 +853,7 @@ onUnmounted(() => {
             @input="debounce('contact-mailserver', () => saveSettings())"
           />
         </label>
+        -->
       </div>
     </section>
 
@@ -986,7 +991,8 @@ onUnmounted(() => {
    article editor's flag selector and the boxes on the second, so the
    flag centers with the boxes and every label sits directly above its
    own field (contact button label = the enable switch, email subject,
-   then the email group: our email + mail server). The flag column sizes
+   our email; the hidden mail-server field joins the email group once the
+   backend lands). The flag column sizes
    to the flag; when only one language is configured the selector renders
    nothing and the column collapses.
    The boxes are readonly until first interaction (+ vendor ignore
@@ -994,7 +1000,8 @@ onUnmounted(() => {
    matter the autocomplete setting. */
 .msg-grid {
   display: grid;
-  grid-template-columns: auto repeat(4, minmax(0, 1fr));
+  /* The hidden mail-server field (template comment) re-adds a column. */
+  grid-template-columns: auto repeat(3, minmax(0, 1fr));
   align-items: center;
   gap: 0.15rem 0.6rem;
 }

frontend/src/contact-main.js

@@ -315,9 +315,11 @@ function watchThread(t) {
   watchThreads.set(t.id, t)
   watchBadge()
   // No notification for history (the first 'threads' push baselines), the
-  // admin's own replies, non-message updates (prev === last.id), closed
-  // threads — or while the inbox is open (MessagesView notifies then).
-  if (!last || last.admin || prev === last.id || t.closed) return
+  // admin's own replies, non-message updates (prev === last.id — or an
+  // unread:false push, e.g. a read marking for a thread beyond the
+  // baseline cap), closed threads — or while the inbox is open
+  // (MessagesView notifies then).
+  if (!last || last.admin || !t.unread || prev === last.id || t.closed) return
   if (state.open && state.mode === 'admin') return
   notifyMessage(`New message from ${t.name || 'a visitor'}`, messageText(last.html), () =>
     open(bridge, { admin: true })