High memory usage on large notebooks

For this notebook,

~/Downloads/large 
❯ du -sh .
69M	.

~/Downloads/large 
❯ find . -name \*.md | wc -l
4561

Emanote takes ~4.7GB of resident memory. It takes a while (~1m) to load all these files at startup, and but runs fine afterwards. The @Index page is slow to render as well, but that should be addressed by use of sub-index'es as described in https://github.com/srid/emanote/discussions/50