Summary

This PR implements the preview-system refactor for the work planned under issue #157.

The branch replaces the old ad-hoc preview wiring with a structured preview capability model, typed preview carriers, and a registry-driven supplementary-view flow. It also moves vectorscope ownership into the preview subsystem, expands the preview dialog and main-window coordination for live tweaks, and adds broad unit-test coverage around the new preview foundations.

At a high level, this PR:

• introduces explicit preview capability contracts and preview view/carrier types in core and view-types
• adds preview view registry and renderer infrastructure so supplementary tools are selected by supported data type instead of hardcoded wiring
• refactors the GUI preview flow so vectorscope, line scope, and related tools are coordinated by the preview subsystem
• adds live tweak support for chroma sink preview workflows, including dirty-state handling and discard-on-close behavior
• improves Y+C preview handling, including more useful combined-frame rendering and a new Y+C linescope mode
• removes the unused auto chroma decoder option
• adds substantial unit coverage for the new preview model

Type of change

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

Validation

Tested locally with:

cmake --build build -j
ctest --test-dir build --output-on-failure

Results:

• build completed successfully
• ctest passed with 460/460 tests passing and 0 failures
• standard contract-test skips remained skipped as expected

Checklist

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

Related issue

Closes #157