Current resource selection with out-of-scope skipping

Summary

• Implemented branch feature/octopus-import-current-selection for OpenSpec task 3.5.
• Added OutOfScopeResources to OctopusImportDependencyPlan so current configuration planning selects only current variable sets/deployment processes while retaining releases, deployments, server tasks, and frozen process/variable snapshots for preview reporting.
• Updated OctopusImportPreviewPlanner to include out-of-scope resources as Skip preview results with ResourceOutOfScope diagnostics.
• Added unit coverage in OctopusImportDependencyPlannerTests and OctopusImportPreviewPlannerTests.
• Updated local OpenSpec progress tracking to mark task 3.5 complete; openspec/ is ignored locally via .git/info/exclude.
• Scope intentionally excludes task 3.6 validation work and any API/persistence changes.

Test plan

• /usr/local/share/dotnet/dotnet test tests/Squid.UnitTests/Squid.UnitTests.csproj --filter "FullyQualifiedName~Services.OctopusImport" --no-restore --disable-build-servers passed: 129/129.
• /usr/local/share/dotnet/dotnet test tests/Squid.UnitTests/Squid.UnitTests.csproj --no-restore --disable-build-servers passed: 6351/6351.
• git diff --check passed.