Configure Git LFS and migrate large files (tfm-slides)

[davidrsch]

Description:
Configure Git LFS in tfm-slides for large binaries and migrate existing large files to LFS or Releases.

DoD:

• .gitattributes with LFS patterns (e.g., *.hdf5, *.rds, large images) committed
• Historical large files migrated to LFS or moved to a Release
• Build/docs updated to fetch assets as needed