Refactor the 'Detect changed images' step in the build-images workflow to improve robustness and debuggability.
Changes include:
- Pass `inputs.image` via an environment variable (`INPUT_IMAGE`) to avoid potential injection issues or syntax errors in shell scripts.
- Add comprehensive `DEBUG` echo statements to trace the logic flow for both manual and automatic detection paths.
- Use `printf` instead of `echo` for writing to `$GITHUB_OUTPUT` to ensure safer handling of string outputs.
- Remove redundant comments to clean up the script block.
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