Add a searchable combobox control for enum variables

select/radio don't scale to enums with dozens of choices. Reuses the
same cmdk Command/Popover primitives multi-select already uses, just
single-valued instead of an array.

src/components/forms/field-renderer.tsx

@@ -24,6 +24,7 @@ import {
 import { Slider } from "@/components/ui/slider";
 import { Label } from "@/components/ui/label";
 import { MultiSelect } from "./controls/multi-select";
+import { Combobox } from "./controls/combobox";
 import type { ClientVariable } from "@/lib/config/serialize";
 
 export function FieldRenderer({ variable }: { variable: ClientVariable }) {
@@ -211,6 +212,31 @@ export function FieldRenderer({ variable }: { variable: ClientVariable }) {
               </FormItem>
             );
 
+          case "combobox":
+            return (
+              <FormItem>
+                <FormLabel>
+                  {label}
+                  {variable.required && (
+                    <span className="text-destructive"> *</span>
+                  )}
+                </FormLabel>
+                <FormControl>
+                  <Combobox
+                    choices={
+                      variable.type === "enum" ? variable.choices : []
+                    }
+                    value={field.value ?? ""}
+                    onChange={(value) => field.onChange(value)}
+                  />
+                </FormControl>
+                {variable.description && (
+                  <FormDescription>{variable.description}</FormDescription>
+                )}
+                <FormMessage />
+              </FormItem>
+            );
+
           case "radio":
             return (
               <FormItem>