ci: fix Docker image builds

[buligar]

Moves the Docker and CMake workflow fixes out of PR #202 into a separate pull request.

Changes:

• add fallback Docker Hub namespace handling for CI workflows;
• skip Docker Hub login and image publishing on pull request builds or when the token is unavailable;
• build SDK images from generated package artifacts;
• install OpenCV for non-Linux CI targets;
• simplify SDK image package installation to use generated .deb files.

Validation: not run locally; this PR changes GitHub Actions workflow configuration.