Add SMTP migration

[premtsd-code]

Adds the project SMTP configuration as a new settings resource. Source reads via the typed Project::get() model; destination writes the project doc's smtp map directly (read-then-merge to preserve destination password — source API never exposes it). Stacks on top of #186.

[greptile-apps]

Greptile Summary

This PR introduces SMTP configuration as a new TYPE_SMTP singleton resource within the GROUP_INTEGRATIONS group, supporting Appwrite-to-Appwrite migration of project-level SMTP settings. Password is intentionally excluded from migration (the source API never exposes it), and the destination uses a read-then-merge strategy to preserve any password already stored there.

• New SMTP resource class (Resources/Settings/SMTP.php) models all non-secret SMTP fields with proper defaults and follows the existing Resource contract.
• Source (exportSMTP) reads from the typed Project::get() model and correctly reports the resource count as a fixed 1 for this singleton; error handling uses the (int) $e->getCode() ?: Exception::CODE_INTERNAL pattern consistently.
• Destination (createSMTP) mirrors the createProtocols/createServices read-then-merge pattern and is correctly wired into the integration dispatch switch with status promotion handled by the outer dispatcher.

Confidence Score: 5/5

Safe to merge — the change is a well-scoped singleton migration following established patterns throughout the codebase, with no correctness issues found.

The SMTP resource registration is complete and consistent across Resource.php, Transfer.php, source, destination, and mock adapters. The read-then-merge write strategy mirrors how protocols and services are already handled. Error handling and status promotion follow the same conventions as peer resource types.

No files require special attention.

Important Files Changed

Filename	Overview
src/Migration/Resources/Settings/SMTP.php	New singleton resource class for SMTP config; correctly omits password, uses sensible defaults, and follows the established Resource contract.
src/Migration/Sources/Appwrite.php	Adds exportSMTP() and wires it into exportGroupIntegrations; report hardcodes count to 1 (correct for singleton); error handling properly uses the (int) cast and CODE_INTERNAL fallback.
src/Migration/Destinations/Appwrite.php	createSMTP uses read-then-merge to preserve the destination's stored password; pattern mirrors createProtocols/createServices; status is promoted to SUCCESS by the outer dispatcher.
src/Migration/Resource.php	TYPE_SMTP constant added and registered in the full type list alongside webhook, consistent with existing type ordering.
src/Migration/Transfer.php	TYPE_SMTP added to GROUP_INTEGRATIONS_RESOURCES and the export/import resource arrays; no issues found.
tests/Migration/Unit/Adapters/MockDestination.php	MockDestination updated to support TYPE_SMTP alongside other integration resource types.
tests/Migration/Unit/Adapters/MockSource.php	MockSource updated to expose TYPE_SMTP as a supported resource type.

_{Reviews (8): Last reviewed commit: "Merge branch 'add-policies-migration' in..." | Re-trigger Greptile}