feat(webui): match Migrate tab to app-detail tab design

Give the fleet Overview › Migrate tab the same in-content header + sub-tab
styling the per-app detail tabs use:

- Add a .config-title header (icon + title + description) inside the Migrate
  pane, above the Restore/Peers sub-tabs, and hide the generic floating fleet
  header for Migrate (mirrors how Backups already supplies its own heading).
- Make the .tab-button icon↔label gap explicit (flex + 6px gap) so sub-tabs
  render identically whether or not the markup has whitespace between the
  emoji and name spans; align the Backups sub-tab strip gap to match.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

containers/libreportal/frontend/components/apps/core/html/apps-unified-layout.html

@@ -317,6 +317,13 @@
           <div class="tab-pane" data-tab="improvements" id="ov-pane-improvements"></div>
           <div class="tab-pane" data-tab="backups" id="ov-pane-backups"></div>
           <div class="tab-pane" data-tab="migrate" id="ov-pane-migrate">
+            <!-- In-content header (mirrors the per-app Config tab's .config-title:
+                 icon + title + description sit inside the pane, above the sub-tabs).
+                 The generic fleet header is hidden for this tab (.ov-migrate-active). -->
+            <div class="config-title">
+              <h3>🔀 Migrate</h3>
+              <p>Move apps in from another LibrePortal, and manage the peers you share backup locations with.</p>
+            </div>
             <!-- Cross-host area: nested segmented sub-tabs (Config-tab design). -->
             <div class="tabs-wrapper ov-subtabs">
               <div class="tabs-list">

containers/libreportal/frontend/components/apps/overview/css/overview.css

@@ -135,7 +135,8 @@
 /* The Backups tab mounts the real BackupPage. Its own page-header replaces the
    generic fleet header, and its left sidebar is restyled into a horizontal
    nested tab strip so the whole thing reads as tabs-within-tabs. */
-#overview-view.ov-backups-active .overview-header { display: none; }
+#overview-view.ov-backups-active .overview-header,
+#overview-view.ov-migrate-active .overview-header { display: none; }
 
 #overview-view #ov-pane-backups .backup-layout { display: block; }
 #overview-view #ov-pane-backups .backup-layout > .sidebar {
@@ -164,7 +165,7 @@
   min-width: 0;
   align-items: center;
   justify-content: center;
-  gap: 8px;
+  gap: 6px;
   margin: 0;
   padding: 12px 14px;
   white-space: nowrap;

containers/libreportal/frontend/components/apps/overview/js/overview-manager.js

@@ -117,10 +117,15 @@ class OverviewManager {
 
   _applyTab(id) {
     if (this.tabs) this.tabs.switch(id);
-    // The Backups tab embeds the full backup center, which brings its own header
+    // Backups embeds the full backup center (its own header + nested sub-tab
-    // and a nested sub-tab strip — hide the generic fleet header for it.
+    // strip) and Migrate carries its own in-content .config-title header above
+    // its sub-tabs — both supply their own heading, so hide the generic fleet
+    // header for them.
     const root = document.getElementById('overview-view');
-    if (root) root.classList.toggle('ov-backups-active', id === 'backups');
+    if (root) {
+      root.classList.toggle('ov-backups-active', id === 'backups');
+      root.classList.toggle('ov-migrate-active', id === 'migrate');
+    }
     this.updateHeader(id);
     this.renderTab(id);
     this.current = id;

containers/libreportal/frontend/core/theme/css/base.css

@@ -526,7 +526,14 @@ html[data-theme="nebula"]::after {
   min-width: 0;
   text-align: center;
   white-space: nowrap;
+  /* Lay the icon + label out as flex children with a fixed gap so spacing is
+     identical whether or not the markup has whitespace between the two spans
+     (the per-app Config sub-tabs rely on source whitespace; the Migrate
+     sub-tabs don't — this makes both render the same). */
+  display: flex;
+  align-items: center;
   justify-content: center;
+  gap: 6px;
 }
 
 /* Task Status Indicator */