.tif files rejected as "Unsupported file type" (only .tiff is whitelisted)

`get_supported_files` in `chandra/scripts/cli.py` checks against a hardcoded extension set that includes .tiff but not .tif. Since .tif is the more common spelling on Windows, TIFF files frequently fail with Unsupported file type: .tif even though the model reads them fine after renaming. Fix: add .tif to the supported_extensions set.