- New reference doc covering whitelisted headers, platform-controlled headers,
  validation rules, limits, usage examples, and error codes
- Add header error codes to Workers API error codes table
- Link headers field in API interface to new reference doc

The directory schema expects 'entry' not 'product', and requires an 'id' field.
Without this, the build fails with 'Cannot read properties of undefined (reading group)'
when Head.astro tries to access product.data.entry.group.

- Remove all quarantine system references (email-lifecycle, logs)
- Remove '(work in progress)' from page titles (domains, metrics, postmaster)
- Remove internal timeline note and fix typo in sandboxing partial
- Generalize retry intervals and suppression thresholds (internal details)
- Reword IP reputation to not expose tiered pool architecture
- Remove specific pricing figures
- Remove 'not available' contradiction from local dev sending page

- Remove 'Workers binding only' and 'top-level domain required' limitations
- Add REST API page with endpoint, auth, and curl example
- Link to REST API reference across index, get-started, and API pages
- Subdomains are now supported (removed top-level domain restriction)

- Flesh out rest-api.mdx with tabs (simple, multiple recipients, CC/BCC),
  attachments, custom headers, and error handling sections
- Add REST API curl tab as the first tab on the index.mdx landing page
- Add 'Send your first email with the REST API' section to get-started
- Add REST API curl tab to headers.mdx usage examples
- Update workers-api.mdx intro to cross-link REST API as alternative
- Update limits.mdx to clarify which limits apply to both APIs vs Workers only
- Add REST API note to local-development/sending.mdx
- Add REST API context note to examples/email-sending index
- Fix stale react: field in workers-api.mdx batch template example
- Fix 3 broken links to /email-service/configuration/workers/