feat(ui): add single selection and keyboard navigation to TagsSelect

Add `multiple` prop to support single-value selection
Implement keyboard navigation (Up/Down/Enter) for dropdown options
Replace native select elements with TagsSelect across views

frontend/src/styles/main.css

@@ -251,11 +251,16 @@ select {
 }
 
 .tags-select__option:hover,
+.tags-select__option.active,
 .tags-select__option.selected {
   background: #edf7ef;
   color: #1f5c40;
 }
 
+.tags-select__option.active {
+  box-shadow: inset 0 0 0 2px rgba(31, 111, 80, 0.18);
+}
+
 .tags-select__option.selected {
   font-weight: 800;
 }
@@ -532,6 +537,10 @@ select {
   flex: 1;
 }
 
+.inline-row .tags-select {
+  flex: 1;
+}
+
 .inline-row input {
   width: 90px;
 }