feat(labs): suggest panels in the marker form and let an edit clear fields

The panel field offers the catalog panels in the page language and the
person's own panels, which GET /api/biomarkers now lists as
customPanels (one spelling per folded form). The field stays free
text; a catalog panel typed in any language lands in the same category.

An edit used to omit an emptied panel, context or bound, so the stored
value survived the save. The form now sends null for a field that held
a value and was emptied. A new marker still omits empty fields, and a
field that was empty when the edit began stays out of the body, so a
context the list could not decrypt is never wiped by an unrelated save.

Refs #1349

docs/api/openapi.yaml

@@ -77763,8 +77763,16 @@ components:
           type: array
           items:
             $ref: "#/components/schemas/Biomarker"
+        customPanels:
+          type: array
+          items:
+            type: string
+          description: The caller's panels that are no catalog panel in any language, one spelling per folded form (the most
+            frequent, ties to the alphabetically first), sorted. Suggestions for the panel field; catalog panels are not
+            repeated here.
       required:
         - biomarkers
+        - customPanels
       additionalProperties: false
     Biomarker:
       type: object