Summary

This PR delivers a full GUI unit-testing foundation and follow-on stability fixes, while also reorganizing test infrastructure and updating CI/docs to support that workflow.

What this branch contains:

• Adds a unified test tree under orc-tests and migrates core unit tests into a source-aligned layout.
• Introduces GUI unit tests (logic/model/widget tiers) with presenter-boundary mocks and offscreen dialog coverage.
• Extracts a testable GUI library target from the app so GUI implementation can be linked into tests without coupling to main entrypoint.
• Adds presenter seams/types used by GUI tests (including an interface boundary for project presenter interactions).
• Strengthens render/live-preview coordination and live-tweak behavior (including stale-response and request-order robustness paths covered by tests).
• Expands contract coverage (including project-to-DAG behavior) and adjusts related core/presenter paths needed by the new tests.
• Updates CI to run GUI tests in headless mode and ensures packaging workflows explicitly disable unit/GUI test builds.
• Updates BUILD and TESTING docs for the new test structure and validation gates, and removes superseded duplicated stage-test expectations content.
• Updates Copilot guidance to reflect the new GUI testing expectations.

Overall diff size: 105 files changed, 4018 insertions, 479 deletions.

Type of change

• Bug fix
• New feature
• Refactor
• Documentation
• Other

Validation

Validated on this branch with:

• cmake --build build -j
• ctest --test-dir build --output-on-failure
• Result: 100% tests passed, 0 failed, out of 618 total
• Label summary from ctest run:
  • unit: 523 tests
  • gui: 94 tests
  • mvp: 1 test
  • cli: 3 tests
• GUI test runs use offscreen backend in CI where applicable.

Checklist

• Scope is focused and minimal
• Build passes locally
• Related docs were updated if needed
• Linked issue (if applicable)

Related issue

Closes #164