Add project variable migration support

[premtsd-code]

Summary

Stacks on #183. Adds project-variable as a migrable resource using the Appwrite SDK's Project::listVariables() (source) and a direct dbForProject->createDocument('variables', ...) (destination) that mirrors upstream Project::Variables::Create exactly.

Notes

• Resource::TYPE_PROJECT_VARIABLE = 'project-variable' (kebab) — placed in GROUP_INTEGRATIONS_RESOURCES alongside platform/api-key for minimum changes to other Source/Destination implementations.
• Destination writes resourceType: 'project' (singular, as upstream does for project-scope) with empty resourceInternalId/resourceId and a synthesized search field.
• Secret variables: the SDK strips value on read for secret variables, so secrets will arrive with empty values. Operator re-enters them on the destination side. (Same caveat as API key secrets.)

[greptile-apps]

Greptile Summary

This PR adds project-variable as a migratable resource, stacking on the API-key migration work in #183. It closely follows the existing Platform and ApiKey patterns throughout the source, destination, and resource layers.

• New ProjectVariable resource class with fromArray/jsonSerialize and accessors for key, value, and secret; the source reads from project->listVariables() using the same cursor-based pagination loop as exportApiKeys.
• Destination writes to dbForProject (variables collection) with resourceType = 'project' and empty resourceInternalId/resourceId, mirroring the upstream Project::Variables::Create schema; duplicate detection queries by resourceType + key.
• TYPE_PROJECT_VARIABLE constant and group membership are correctly registered in Resource.php, Transfer.php, and both the source/destination supportedResources lists.

Confidence Score: 4/5

Safe to merge; the only open question is whether a platform project-cache purge is needed after writing to dbForProject.

The implementation faithfully mirrors the ApiKey/Platform patterns. The one thing that stands out is that createApiKey and createPlatform both call dbForPlatform->purgeCachedDocument('projects', ...) after writing, but createProjectVariable does not. If the platform project cache includes any variable-related metadata this omission could leave stale data, but it may also be intentional since variables live in dbForProject rather than dbForPlatform. The rest of the code — pagination, duplicate detection, resource registration — is consistent and correct.

src/Migration/Destinations/Appwrite.php — the createProjectVariable method is the only spot worth a second look (the cache purge question).

Important Files Changed

Filename	Overview
src/Migration/Destinations/Appwrite.php	Adds createProjectVariable writing to dbForProject; correctly checks for duplicates and handles DuplicateException, but omits the purgeCachedDocument call present in both createApiKey and createPlatform.
src/Migration/Sources/Appwrite.php	Adds exportProjectVariables that uses cursor-based pagination, closely mirroring the existing exportApiKeys implementation.
src/Migration/Resources/Integrations/ProjectVariable.php	New resource class mirroring the ApiKey pattern; clean with fromArray, jsonSerialize, and accessors for key, value, and secret fields.
src/Migration/Resource.php	Adds TYPE_PROJECT_VARIABLE = 'project-variable' constant and includes it in the all-types list; straightforward and consistent.
src/Migration/Transfer.php	Adds TYPE_PROJECT_VARIABLE to GROUP_INTEGRATIONS_RESOURCES alongside platform and api-key; minimal and correct.

_{Reviews (1): Last reviewed commit: "Add project variable migration support" | Re-trigger Greptile}

[greptile-apps]

Both createPlatform and createApiKey call $this->dbForPlatform->purgeCachedDocument('projects', $this->project) after writing their documents. createProjectVariable omits this. If the platform's projects document caches any project-level metadata (variable counts, etc.), created variables won't be reflected until the cache naturally expires. Worth verifying against the upstream Project::Variables::Create implementation to confirm whether the purge is needed here too.

Suggested change

	} catch (DuplicateException) {
	$resource->setStatus(Resource::STATUS_SKIPPED, 'Project variable already exists');
	return false;
	}
	return true;
	}
	private function validateFieldsForIndexes(Index $resource, UtopiaDocument $table, array &$lengths)
	} catch (DuplicateException) {
	$resource->setStatus(Resource::STATUS_SKIPPED, 'Project variable already exists');
	return false;
	}
	$this->dbForPlatform->purgeCachedDocument('projects', $this->project);
	return true;
	}
	private function validateFieldsForIndexes(Index $resource, UtopiaDocument $table, array &$lengths)