- Introduce `shiftRadius` to allow positional tolerances by searching
a local neighborhood, absorbing sub-pixel shifts and MSAA quirks.
- Introduce `blurRadius` to apply local area averaging, ignoring
high-frequency noise like hardware dithering.
- Enhance `ImageDiffResult` to include an `averageError` array and
a 10-bin `errorHistogram` for actionable failure debugging.
- Update Android JNI bindings (`ImageDiff.java` and `ImageDiff.cpp`)
to propagate the new error distribution statistics to Java callers.
- Update C++ unit tests to cover the new heuristic options.
- Document the new parameters and JSON result format in README.md.
- Add synthetic image generation tests in `tools/diffimg/tests/` to
validate the CLI tool's handling of spatial shifts and dithering.
