[Fix] Hide managed Email configuration on Roomote Cloud

[roomote-roomote]

​Opened on behalf of @mrubens. View the task or mention @roomote-roomote for follow-up asks.

What changed

• treats R_CLOUD_ENABLED as the managed Email discriminator
• shows the managed inbox address, webhook health, and an explicit unavailable state without rendering AgentMail setup or removal controls
• rejects direct AgentMail save and clear mutations before provider or database work on Cloud deployments
• preserves the existing configurable AgentMail flow for self-hosted deployments
• documents the managed Cloud behavior and default roomote.me address

Why this change was made

Roomote Cloud owns the AgentMail credentials and webhook lifecycle. Tenant administrators should be able to see whether managed Email is healthy or unavailable without being able to replace or remove Cloud-owned configuration.

Impact

Cloud deployments get a status-only Email settings surface with server-enforced mutation protection. Self-hosted operators retain the existing API-key setup, reconciliation, and disconnect behavior.

Related PRs

• Roomote-Cloud managed Email provisioning

[roomote-community]

No new code issues found. See task

• Cloud email unavailable state missing (apps/web/src/components/settings/CommsProviderSection.tsx:650)

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