Merged PR 2242: Refactor: New Appeal flow structural cleanup (Slices 1–8, no behaviour change)

## Summary

This PR merges the completed new-appeal refactor stream (Slices 1–8) into SIPS-Development.

This refactor was executed in controlled slices with regression validation at each step.

## Scope

Structural and readability improvements only:
- XML/form derivation extraction
- payload and file helper extraction
- side-effect facade introduction
- BuildSection and BuildCheckSection decomposition
- BuildCheckRow formatter map refactor
- nested prop boundary cleanup
- start-flow cleanup (CreateCase / AboutYou)

## Behaviour

No intended behavioural changes.

The following were explicitly preserved:
- S78 journey behaviour
- payload shapes and field names/ids
- HASCAS mapping logic
- appellant/agent branching
- validation rules and messages
- redirect/query parameters (`lpa`, `apt`, `id`)
- navigation and side-effect sequencing
- EN/CY output parity

## Validation

Full regression has been performed on:
- start flow (CreateCase / AboutYou)
- save and resume flows
- file upload handling
- check answers rendering
- submit/finalisation sequence
- confirmation flow
- CRM insertion path
- EN/CY parity

Additional checks:
- docsOffline branch behaviour
- completion and partial-save email paths
- negative-path validation scenarios
- lint (warnings baseline unchanged)

## Risk

Low:
- changes are structural only
- no business logic changes
- no contract changes

## Rollback

Safe rollback via reverting this merge commit.

## Notes

This refactor reduces coupling and prepares the new-appeal flow for future appeal-type expansion.

Related work items: #22570, #22576, #22577, #22583, #22586, #22587, #22588, #22590

components/newappeal/aboutyou.js

@@ -262,7 +262,7 @@ const RenderRadio = ({
                                                       {
                                                           ["documentCheckList_" +
                                                           id]:
-                                                              custom.requiredDocumentLabel,
+                                                              custom.requiredDocumentLabel
                                                       }
                                                   ))
                                                 : delete docListObj[
@@ -297,7 +297,7 @@ function Radiofield(props) {
         formProps,
         parentFieldShowOnValue,
         validation,
-        hint,
+        hint
     } = props;
 
     const router = useRouter();
@@ -438,22 +438,25 @@ let AboutYou = (props) => {
 
     const router = useRouter();
     const { locale } = router;
+    const isWelsh = router.locale == "cy";
 
     const {
         onSubmit,
         handleSubmit,
         appellantAgentValue,
         setFormStep,
-        updateField,
+        updateField
     } = props;
 
     const [isAgent, setIsAgent] = useState(false);
+    const isAgentSelected = appellantAgentValue == "846040001";
+    const isAppellantSelected = appellantAgentValue == "846040000";
 
-    const yesNo = router.locale == "cy" ? ["Ydw", "Na"] : ["Yes", "No"];
-    const appellantAgent =
-        router.locale == "cy" ? ["Apelydd", "Asiant"] : ["Appellant", "Agent"];
-    const contactPref =
-        router.locale == "cy" ? ["Ebost", "Post"] : ["Email", "Post"];
+    const yesNo = isWelsh ? ["Ydw", "Na"] : ["Yes", "No"];
+    const appellantAgent = isWelsh
+        ? ["Apelydd", "Asiant"]
+        : ["Appellant", "Agent"];
+    const contactPref = isWelsh ? ["Ebost", "Post"] : ["Email", "Post"];
 
     const required = (value) =>
         value ? undefined : t("newappeal:is-required-label");
@@ -493,7 +496,7 @@ let AboutYou = (props) => {
     };
 
     const handlePartialUpdate = () => {
-        if (appellantAgentValue == "846040001" && isAgent == false) {
+        if (isAgentSelected && isAgent == false) {
             updateField("caseForm", "pinswg_appellantfirstname", "");
             updateField("caseForm", "pinswg_appellantlastname", "");
             updateField("caseForm", "pinswg_appellantemailaddress", "");
@@ -570,7 +573,7 @@ let AboutYou = (props) => {
                 errorMsg={t("newappeal:select-an-option-label")}
                 hint={t("newappeal:about-you-who-are-you-hint-label")}
             />
-            {appellantAgentValue == "846040000" && (
+            {isAppellantSelected && (
                 <>
                     <h2 className="govuk-heading-s">
                         {t("newappeal:about-you-appellant-contact-details")}
@@ -668,7 +671,7 @@ let AboutYou = (props) => {
                     />
                 </>
             )}
-            {appellantAgentValue == "846040001" && (
+            {isAgentSelected && (
                 <>
                     <h2 className="govuk-heading-s">
                         {t("newappeal:about-you-appellant-contact-details")}
@@ -891,15 +894,15 @@ const mapStateToProps = (state) => {
             pinswg_appellantaddress:
                 state.accountDetails.accountDetails.address1_composite,
             pinswg_appellantphonenumber:
-                state.accountDetails.accountDetails.telephone1,
-        },
+                state.accountDetails.accountDetails.telephone1
+        }
     };
 };
 
 const mapDispatchToProps = (dispatch) => {
     return {
         updateField: (form, field, newValue) =>
-            dispatch(change(form, field, newValue)),
+            dispatch(change(form, field, newValue))
     };
 };
 
@@ -915,7 +918,7 @@ AboutYou = connect((state) => {
     const appellantAgentValue = selector(state, "pinswg_appellantagent");
 
     return {
-        appellantAgentValue,
+        appellantAgentValue
     };
 })(AboutYou);
 
@@ -928,6 +931,6 @@ export default connect(
     reduxForm({
         form: "caseForm",
         enableReinitialize: true, // this is needed!!
-        destroyOnUnmount: false,
+        destroyOnUnmount: false
     })(AboutYou)
 );