Add per-item Apply button to queued resolution selected bar

Refactor queue_methods.js to split applyPendingResolutions into
applyQueuedByKey (per-item) and applyPendingResolutionList (shared
implementation). Add an Apply button alongside the Remove button in
the selected resolution bar, wired to applyQueuedByKey with loading
state. Update CSS for .mr-selected-actions layout and .mr-btn-primary
styling in the detail pane.

web/css/resolver-shell.css

@@ -523,6 +523,14 @@
     text-overflow: ellipsis;
 }
 
+.mr-selected-actions {
+    display: inline-flex;
+    flex: 0 0 auto;
+    align-items: center;
+    gap: var(--mr-spacing-8);
+    margin-left: auto;
+}
+
 .mr-inline-note-link {
     cursor: pointer;
     color: var(--mr-accent-blue);