centralise repertoire filter column rendering

- shared repFilterEntry() and  config array
- shared repFilterEntry() and $filterColumns config array
- fix single-valued FK fading via full intersection

app/public/assets/css/common.css

@@ -416,6 +416,7 @@ main {
         opacity 0.15s,
         box-shadow 0.15s,
         filter 0.15s;
+    width: fit-content;
 }
 
 .btn:hover {
@@ -563,7 +564,7 @@ main {
    ============================================================ */
 
 fieldset {
-    background: var(--bg-secondary);
+    /*background: var(--bg-secondary);*/
     border: 1px solid var(--border-primary);
     border-radius: 4px;
     padding: var(--space-m);