fix: stop LFS pointer warnings for skill outputs

[dajiaohuang]

Summary

• Keep the four affected example output files as regular Git blobs.
• Add path-specific attribute overrides so Git LFS no longer expects pointer objects for those files.
• Leave the existing PNG/GIF LFS rules in place for other paths.

Fixes #500

Validation

• The four affected paths report filter, diff, merge, and text as unset with git check-attr -a.
• git lfs status reports no objects to be committed or pushed.
• git diff --check passes.
• The branch is based directly on current master (e31dadd).