refactor(core): Consolidate secret provider connection response types into api-types (no-changelog)

[everettbu]

Mirror of n8n-io/n8n#26114
Original author: alielkhateeb

---

Summary

Removes the local SecretsProvidersResponses namespace declaration (secrets-providers.responses.ee.ts) and moves the response types directly into ``@n8n/api-types as proper exported types.

Changes:

• SecretProviderConnection — full connection response (settings + secrets, no isEnabled)
• SecretProviderConnectionListItem — lightweight list item (no settings, secrets, or isEnabled)
• Both controllers and the service now import these types directly from ``@n8n/api-types

No behaviour change — this is a type-level refactor only.

Related Linear tickets, Github issues, and Community forum posts

https://linear.app/n8n/issue/LIGO-266

Review / Merge checklist

• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)