Improve form validation accessibility

[web3blind]

Summary

• Moves focus to the visible form error summary when validation errors first appear on the current form page.
• Removes aria-invalid from valid form controls and only renders aria-invalid="true" when the field has validation errors.
• Adds the field error message id to aria-describedby when errors are present, so the invalid field is programmatically associated with its error text.

Related issues

Addresses the Vue form stack used by the OJS submission workflow:

• [A11Y] OJS Editorial View - Focus not moving to validation error messages in new submission workflow pkp-lib#12599
• [A11Y] OJS Editorial View - Misuse of aria-invalid on fields in Start a Submission form pkp-lib#12837

Verification

• npm test -- --run — 6 files / 58 tests passed.
• npx eslint src/components/Form/FormErrors.vue src/components/Form/FormPage.vue src/components/Form/fields/FieldBase.vue src/components/Form/fields/FieldText.vue src/components/Form/fields/FieldTextarea.vue src/components/Form/fields/FieldSelect.vue src/components/Form/fields/FieldDate.vue src/components/Form/fields/FieldOptions.vue src/components/Form/fields/FieldRadioInput.vue src/components/Form/fields/FieldMetadataSetting.vue src/components/Form/fields/FieldPubId.vue src/components/Form/fields/FieldArchivingPn.vue — 0 errors; existing warnings only.
• git diff --check — passed.

Note: npm run lint currently exits before linting because the upstream script passes --ignore-path while this checkout uses eslint.config.js; the targeted ESLint command above avoids that script-level blocker.