Updates the `build-images` workflow to robustly detect and validate changes to image directories.
Changes:
- Implements strict validation to ensure detected image directories exist and contain a `Dockerfile` before adding them to the build matrix.
- Normalizes logic for both manual inputs and automatic git-diff detection using a temporary file (`valid_images.txt`) to collect targets.
- Adds specific checks to warn if a manually specified image is missing or invalid.
- Prevents the build job from failing or running unnecessarily if an empty image name is passed to the matrix by adding an early exit condition.
Updates the image building workflow to improve reliability and readability.
Changes:
- Replaced the complex `moby/buildkit` container-in-container execution with standard Docker build and push steps.
- Added explicit checkout, login, and build steps to the job matrix.
- Improved the change detection logic:
- Added input sanitization (whitespace trimming) for manually triggered builds.
- Added comments explaining the directory diff logic.
- Updated job titles and comments to English for consistency (e.g., "Detect modified images" instead of "Détection des images modifiées").
- Added `fail-fast: false` to the matrix strategy so one failed build doesn't stop others.
