Add project variable migration wizard support

[premtsd-code]

Summary

Stacks on the api-key console PR. Adds project-variable as its own top-level group in the migration wizard, parallel to platforms and api-keys.

Cross-repo

• Add project variable migration support utopia-php/migration#184
• Add project variable migration support appwrite#12313
• appwrite-labs/cloud#4034

[greptile-apps]

Greptile Summary

This PR adds project-variable as a new top-level migration resource group (settings) in the wizard, parallel to platforms and api-keys, covering the store type declarations, form↔resource conversion logic, rendering guards, and label/description maps.

• migration.ts extends MigrationResource, MigrationResources, ResourcesFriendly, providerResources.appwrite, and both migrationFormToResources/resourcesToMigrationForm with the new project-variable entry, following the same patterns used for api-key and platform.
• resource-form.svelte adds a settings branch to shouldRenderGroup and a settings → 'project-variable' entry to getReportKey, keeping display logic consistent with other groups.
• importReport.svelte registers settings in labelMap and descriptionMap; because the group has no child keys, the component takes the simple-checkbox path where only the label is shown and the descriptionMap entry goes unused (the same dead-code pattern exists for backups and storage).

Confidence Score: 5/5

Safe to merge — the change is additive and follows established patterns already used for platform and api-key.

All three files introduce project-variable / settings by mirroring the exact patterns used for the prior api-key and platform additions. The form-to-resource and resource-to-form round-trip is correctly implemented, the render guard is consistent, and no existing paths are modified.

No files require special attention.

Important Files Changed

Filename	Overview
src/lib/stores/migration.ts	Adds project-variable to the MigrationResource type, MigrationResources enum, ResourcesFriendly, providerResources (appwrite only), and both form↔resource conversion functions; follows the same pattern as api-key and platform
src/routes/(console)/(migration-wizard)/resource-form.svelte	Adds a settings guard to shouldRenderGroup and a settings → 'project-variable' mapping in getReportKey; consistent with existing group handling
src/routes/(console)/project-[region]-[project]/settings/migrations/(import)/importReport.svelte	Adds settings entries to labelMap and descriptionMap; description text is not surfaced to users through the current rendering path (no-children simple-checkbox branch), which is a pre-existing pattern also affecting backups and storage

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