Implement column selector customizer popover for chronological events logbook

client/src/App.css

@@ -6464,3 +6464,62 @@ body.app-tour-active .feedback-modal-overlay--tour .disclaimer-modal-panel {
 .member-editor-card .accordion-header:hover {
   background: var(--app-surface-hover, rgba(255, 255, 255, 0.03));
 }
+
+/* Column Selector / Customizer Popover */
+.column-selector-popover {
+  position: absolute;
+  top: 40px;
+  right: 0;
+  width: 240px;
+  max-height: 400px;
+  overflow-y: auto;
+  padding: 16px;
+  border-radius: 12px;
+  background: var(--app-surface-alt, rgba(18, 20, 26, 0.98));
+  border: 1px solid var(--app-border, rgba(255, 255, 255, 0.1));
+  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.5);
+  z-index: 100;
+  display: flex;
+  flex-direction: column;
+  gap: 12px;
+  text-align: left;
+}
+
+.column-selector-title {
+  font-size: 13.5px;
+  font-weight: 600;
+  color: var(--app-accent, #fbbf24);
+  margin: 0;
+  padding-bottom: 6px;
+  border-bottom: 1px solid var(--app-border-subtle, rgba(255, 255, 255, 0.06));
+}
+
+.column-selector-list {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+}
+
+.column-selector-item {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  cursor: pointer;
+  font-size: 13px;
+  color: var(--app-text-muted, #cbd5e1);
+  padding: 4px 6px;
+  border-radius: 6px;
+  transition: background-color 0.15s ease, color 0.15s ease;
+}
+
+.column-selector-item:hover {
+  background: var(--app-surface-hover, rgba(255, 255, 255, 0.04));
+  color: var(--app-text, #ffffff);
+}
+
+.column-selector-item input[type="checkbox"] {
+  width: 14px;
+  height: 14px;
+  cursor: pointer;
+  accent-color: var(--app-accent, #fbbf24);
+}