feat: improve modal sidebar hierarchy, collapse add-to-series, in-context feedback

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/static/style.css

@@ -598,6 +598,73 @@ header {
   .modal-close-hint { display: none; }
 }
 
+/* Modal sidebar sections */
+.modal-sidebar-section {
+  padding: 0.75rem 0;
+  border-bottom: 1px solid rgba(255, 255, 255, 0.07);
+}
+.modal-sidebar-section:last-child {
+  border-bottom: none;
+}
+
+/* Series toggle button (for "Add to Series" collapsed state) */
+.modal-series-toggle {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  width: 100%;
+  background: none;
+  border: none;
+  color: var(--text-muted);
+  font-size: 0.85rem;
+  cursor: pointer;
+  padding: 0.25rem 0;
+  transition: color 0.15s ease;
+}
+.modal-series-toggle:hover {
+  color: var(--text-dim);
+}
+.modal-series-toggle .toggle-arrow {
+  transition: transform 0.15s ease;
+  font-size: 0.9rem;
+}
+.modal-series-toggle.open .toggle-arrow {
+  transform: rotate(90deg);
+}
+
+.add-series-body {
+  margin-top: 0.5rem;
+}
+
+/* In-context feedback label */
+.tag-feedback {
+  font-size: 0.75rem;
+  color: var(--flash-success);
+  opacity: 0;
+  transition: opacity 0.2s ease;
+  display: inline-block;
+  margin-left: 0.4rem;
+}
+.tag-feedback.visible {
+  opacity: 1;
+}
+.tag-feedback-inline {
+  display: block;
+  margin-left: 0;
+  margin-top: 0.3rem;
+  min-height: 1.1em;
+}
+
+/* Tag chip remove button — hidden at rest, visible on hover */
+.tag-chip .x {
+  opacity: 0;
+  transition: opacity 0.15s ease;
+  margin-left: 4px;
+}
+.tag-chip:hover .x {
+  opacity: 1;
+}
+
 /*------------------------------------------------------------------------------
   Tag overlays & editor
 ------------------------------------------------------------------------------*/