docs: fix stale FileRef.kind comment to match fingerprint_kind_from_metadata

Listed outdated kind values ("raw_fp16" / "nvfp4") that the detector never
returns; corrected to the real set ("raw_highprec" / "nvfp4_disk" / "raw_fp4" /
"raw_int8" ...) plus the force_kind "bundled_checkpoint". Comment-only.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>