Balch PDF: swap 142 MB version for 3.6 MB version; drop from LFS

User-supplied smaller PDF replaces the bulky one. Now under the 50 MB
threshold so it doesn't need LFS tracking — removed from .gitattributes
and re-added as a regular blob via git rm --cached + git add.

Author: rhiju

.gitattributes

@@ -1,3 +1,2 @@
 /assets/pdfs/Kretsch_Nature_ComplexWaterNetworks_2025.pdf filter=lfs diff=lfs merge=lfs -text
 /assets/pdfs/Kretsch_OrnateRNA_2025.pdf filter=lfs diff=lfs merge=lfs -text
-assets/pdfs/Balch_NatComm_2026.pdf filter=lfs diff=lfs merge=lfs -text