fix(campaign): stabilize message preview overlays

webui/src/styles/campaign-workspace.css

@@ -1096,9 +1096,36 @@
 }
 
 /* Shared message preview overlay --------------------------------------- */
+.message-preview-modal {
+  width: min(920px, 100%);
+  height: min(780px, calc(100dvh - 48px));
+  max-height: calc(100dvh - 48px);
+}
+
+.message-preview-modal .modal-header {
+  min-width: 0;
+}
+
+.message-preview-modal .modal-header h2 {
+  min-width: 0;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
 .message-preview-modal .modal-body {
+  flex: 1 1 auto;
+  min-height: 0;
   display: grid;
+  align-content: start;
   gap: 1rem;
+  overflow: auto;
+  scrollbar-gutter: stable;
+}
+
+.message-preview-modal .modal-footer {
+  align-items: center;
+  min-height: 68px;
 }
 
 .message-preview-modal .message-display-body,
@@ -1156,6 +1183,38 @@
   font-weight: 700;
   color: var(--text-primary);
 }
+
+@media (max-width: 720px), (max-height: 700px) {
+  .message-preview-backdrop {
+    padding: 8px;
+  }
+
+  .message-preview-modal {
+    width: 100%;
+    height: calc(100dvh - 16px);
+    max-height: calc(100dvh - 16px);
+  }
+
+  .message-preview-modal .modal-header {
+    min-height: 52px;
+    padding-inline: 14px;
+  }
+
+  .message-preview-modal .modal-body {
+    padding: 14px;
+  }
+
+  .message-preview-modal .modal-footer {
+    min-height: 58px;
+    padding: 10px 14px;
+  }
+
+  .message-preview-modal .message-display-body,
+  .message-preview-modal .message-display-html-frame {
+    height: clamp(210px, 38dvh, 360px);
+    max-height: clamp(210px, 38dvh, 360px);
+  }
+}
 .attachment-source-path-cell {
   display: grid;
   gap: 5px;