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 adds SMTP configuration as a new singleton migration resource, stacking on top of the policies migration. The source reads SMTP settings via the typed Project::get() model, and the destination uses a read-then-merge pattern so the destination's stored password is never overwritten (since the source API never exposes it).

• SMTP.php introduces a clean singleton resource class with typed constructor, fromArray, jsonSerialize, and the full set of accessors.
• Sources/Appwrite.php adds exportSMTP() and wires it into exportGroupIntegrations with proper (int) $e->getCode() ?: Exception::CODE_INTERNAL error handling.
• Destinations/Appwrite.php adds createSMTP() with the read-then-merge approach and routes it in importIntegrationsResource; Transfer.php and Resource.php register the new type in all expected constants.

Confidence Score: 5/5

Safe to merge; the read-then-merge pattern correctly preserves the destination password, and all routing constants are consistently updated across the five changed files.

The new SMTP path is a straightforward singleton migration: export reads typed model fields directly, import merges only the non-secret fields into the destination document, and the cache is purged after the update. No data-loss or auth boundary issues were found.

src/Migration/Sources/Appwrite.php — minor structural inconsistency in the SMTP try/catch block compared to the other blocks in exportGroupIntegrations.

Important Files Changed

Filename	Overview
src/Migration/Resources/Settings/SMTP.php	New singleton resource class for project SMTP config; clean model with proper accessors, fromArray, and jsonSerialize.
src/Migration/Sources/Appwrite.php	Adds exportSMTP() using typed Project model fields; the new SMTP try/catch block uses inverted nesting (try wrapping the if) compared to the consistent if-wrapping-try pattern used for Platform, API_KEY, and Webhook.
src/Migration/Destinations/Appwrite.php	Adds createSMTP() using a correct read-then-merge pattern that preserves the destination password; import routing placed correctly in importIntegrationsResource.
src/Migration/Resource.php	Adds TYPE_SMTP constant and registers it in the all-types array; correct placement alongside other integration types.
src/Migration/Transfer.php	Adds TYPE_SMTP to GROUP_INTEGRATIONS_RESOURCES and the master resource list; consistent with the new resource's getGroup() return value.

_{Reviews (6): Last reviewed commit: "Move SMTP into integrations group (exter..." | Re-trigger Greptile}