T3: CI / ctest integration for logoscore tests

[xAlisher]

Context

Part of logoscore test epic #88.

Steps

1. Add tests/integration/ as ctest target in CMakeLists.txt
2. Skip gracefully if logoscore not found in Nix store
3. Document run procedure in README

Success criteria

• ctest picks up integration tests when logoscore available
• ctest skips gracefully when logoscore not found
• README documents how to run integration tests