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/buildCheckSection/ConfirmationCheckboxGroup.js

@@ -0,0 +1,63 @@
+const ConfirmationCheckboxGroup = ({
+    downloadAppealForm,
+    onDownloadChange,
+    onConfirmChange,
+    downloadLabel,
+    confirmLabel,
+    paragraphOne,
+    paragraphTwo,
+    paragraphTwoLink
+}) => {
+    return (
+        <div className="govuk-form-group ">
+            <fieldset className="govuk-fieldset">
+                <div className="govuk-checkboxes govuk-checkboxes--small">
+                    <div className="govuk-checkboxes__item">
+                        <input
+                            name="pinswg_downloadAppealForm"
+                            id="pinswg_downloadAppealForm"
+                            type="checkbox"
+                            className="govuk-checkboxes__input"
+                            checked={downloadAppealForm}
+                            onChange={onDownloadChange}
+                        />
+                        <label
+                            className="govuk-label govuk-checkboxes__label"
+                            htmlFor="pinswg_downloadAppealForm"
+                        >
+                            {downloadLabel}
+                        </label>
+                    </div>
+                </div>
+                <div className="govuk-checkboxes govuk-checkboxes--small">
+                    <div className="govuk-checkboxes__item">
+                        <input
+                            name="pinswg_checkconfirmation"
+                            id="pinswg_checkconfirmation"
+                            type="checkbox"
+                            className="govuk-checkboxes__input"
+                            value=""
+                            onChange={onConfirmChange}
+                        />
+                        <label
+                            className="govuk-label govuk-checkboxes__label"
+                            htmlFor="pinswg_checkconfirmation"
+                        >
+                            {confirmLabel}
+                        </label>
+                    </div>
+                </div>
+            </fieldset>
+            <div>
+                <p className="govuk-body">{paragraphOne}</p>
+            </div>
+            <div>
+                <p className="govuk-body">
+                    {paragraphTwo} {paragraphTwoLink}
+                </p>
+            </div>
+        </div>
+    );
+};
+
+export default ConfirmationCheckboxGroup;