refactor(knowledge_compiler): derive variant from template kind via single template id (#17630)

## Summary

Refactor the Go `KnowledgeCompilerComponent` so its parameter is a
**single string template id** instead of a DSL-level `variant` (or
plural group id list). The `variant` is no longer in the DSL — it is now
**derived at runtime from the resolved compilation template's `kind`
field**.

This aligns the Go ingestion port with the frontend Compiler operator,
which emits a singular `compilation_template_group_id` and does not
write `variant` into the generated `compiler.json`.

web/src/pages/agent/canvas/node/compilation-node.tsx

@@ -10,7 +10,7 @@ export function CompilationNode({ ...props }: NodeProps<IRagNode>) {
   const { data } = props;
   const { t } = useTranslation();
   const options = useCompilationTemplateGroupOptions();
-  const groupId = get(data, 'form.compilation_template_group_ids');
+  const groupId = get(data, 'form.compilation_template_group_id');
   const groupName =
     options.find((option) => option.value === groupId)?.label ?? groupId;
 

web/src/pages/agent/constant/pipeline.tsx

@@ -362,7 +362,7 @@ export const initialExtractorValues = {
 };
 
 export const initialCompilationValues = {
-  compilation_template_group_ids: [],
+  compilation_template_group_id: '',
   outputs: {
     chunks: { type: 'Array<Object>', value: [] },
   },

web/src/pages/agent/form/compilation-form/index.tsx

@@ -13,7 +13,7 @@ import { FormWrapper } from '../components/form-wrapper';
 import { Output } from '../components/output';
 
 export const FormSchema = z.object({
-  compilation_template_group_ids: z.string().optional(),
+  compilation_template_group_id: z.string().optional(),
 });
 
 export type CompilationFormSchemaType = z.infer<typeof FormSchema>;
@@ -33,7 +33,7 @@ const CompilationForm = ({ node }: INextOperatorForm) => {
   return (
     <Form {...form}>
       <FormWrapper>
-        <CompilationTemplateFormField name="compilation_template_group_ids"></CompilationTemplateFormField>
+        <CompilationTemplateFormField name="compilation_template_group_id"></CompilationTemplateFormField>
         <Output list={outputList}></Output>
       </FormWrapper>
     </Form>