contact messages: unified overlay, corner ✉️ icon for everyone

The admin inbox leaves the short-lived /_m page and joins the visitor panel as one overlay (ContactOverlay shell over paskia's shared blur backdrop, centered dialog, full-screen on mobile): the corner ✉️ icon opens the visitor thread for visitors and the wider sidebar inbox for admins, while {contact:} trigger buttons always open the visitor side so admins can test both. The icon highlights unread state without extra connections: visitors via localStorage seen/last-admin timestamps, admins via the contact_unread count added to the /_api/settings probe, both kept live by the bundle once loaded. MessagesView owns its admin socket only while the overlay is open.

frontend/src/assets/pagerite.css

@@ -407,6 +407,47 @@ body.editing #sidebar {
   text-decoration: none;
 }
 
+/* The corner ✉️ (docs/messages.md) is in the pens row for everyone, so
+   needs its own positioning context for the unread markers: the same
+   accent dot as the trigger buttons (visitors: a new reply) or a count
+   pill (admins: unanswered threads). The marker lifts the icon out of the
+   icon-btn dimming so it reads clearly. */
+.contact-icon {
+  position: relative;
+}
+
+.contact-icon.has-unread {
+  opacity: 1;
+}
+
+.contact-icon.has-unread::after {
+  content: "";
+  position: absolute;
+  top: -0.2em;
+  right: -0.25em;
+  width: 0.5em;
+  height: 0.5em;
+  border-radius: 50%;
+  background: var(--accent);
+  box-shadow: 0 0 0 0.12em var(--bg);
+}
+
+.contact-icon .n {
+  position: absolute;
+  top: -0.5em;
+  right: -0.7em;
+  min-width: 1.3em;
+  padding: 0.05em 0.3em;
+  border-radius: 1em;
+  background: var(--accent);
+  color: var(--bg);
+  font-size: 0.62em;
+  font-weight: 700;
+  line-height: 1.3;
+  text-align: center;
+  opacity: 1;
+}
+
 #sidebar {
   grid-column: 1;
   /* Pinned to the page's start edge (not the article's) and kept in view