fix(dashboard) Standardize heading levels for consistent hierarchy (#13861)

## Summary

**What** — What changes are introduced in this PR?

This PR standardizes heading levels across dashboard components to maintain proper semantic HTML hierarchy.

**Why** — Why are these changes relevant or necessary?  

*Please provide answer here*

**How** — How have these changes been implemented?

- Added optional `headingLevel` prop `"h1" | "h2" | "h3"` to `DataTable` component with default value of `"h1"`

- Modified `Heading` component usage to explicitly specify the appropriate level based on context

**Testing** — How have these changes been tested, or how can the reviewer test the feature?

*Please provide answer here*

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## Checklist

Please ensure the following before requesting a review:

- [x] I have added a **changeset** for this PR
    - Every non-breaking change should be marked as a **patch**
    - To add a changeset, run `yarn changeset` and follow the prompts
- [ ] The changes are covered by relevant **tests**
- [x] I have verified the code works as intended locally
- [ ] I have linked the related issue(s) if applicable

packages/admin/dashboard/src/routes/api-key-management/api-key-management-detail/components/api-key-sales-channel-section/api-key-sales-channel-section.tsx

@@ -56,6 +56,7 @@ export const ApiKeySalesChannelSection = ({
         filters={filters}
         commands={commands}
         heading={t("salesChannels.domain")}
+        headingLevel="h2"
         getRowId={(row) => row.id}
         rowCount={count}
         isLoading={isPending}

packages/admin/dashboard/src/routes/api-key-management/api-key-management-list/components/api-key-management-list-table/api-key-management-list-table.tsx

@@ -53,7 +53,7 @@ export const ApiKeyManagementListTable = ({
     <Container className="divide-y p-0">
       <div className="flex items-center justify-between px-6 py-4">
         <div>
-          <Heading level="h2">
+          <Heading level="h1">
             {keyType === "publishable"
               ? t(`apiKeyManagement.domain.publishable`)
               : t("apiKeyManagement.domain.secret")}