The cached inbox template endpoint currently serves only native WhatsApp
channels. This draft extends the same read-only endpoint to Twilio
WhatsApp inboxes and adds last-sync metadata for both providers, so the
template listing can use one stable contract without making provider
requests.
Non-WhatsApp inbox behavior remains unchanged.
Related:
https://linear.app/chatwoot/issue/PLA-193/add-whatsapp-template-listing-to-account-settings
### Things to know
- This is stack 1 of 2 and contains only the API contract needed by the
settings UI in #15312.
- Template data remains cache-only; the endpoint does not call Meta or
Twilio.
- Native WhatsApp templates are filtered by `name`; Twilio Content
Templates are filtered by `friendly_name`.
### How to test
1. Request the message templates endpoint for a native WhatsApp inbox
and confirm it returns the cached templates plus `meta.last_updated_at`.
2. Request it for a Twilio WhatsApp inbox and confirm it returns cached
Content Templates plus `meta.last_updated_at`.
3. Pass a template name and confirm only the matching provider template
is returned.
4. Request it for a non-WhatsApp inbox and confirm the endpoint returns
an unprocessable entity response.
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Co-authored-by: Muhsin <12408980+muhsin-k@users.noreply.github.com>