todo.normalise-tags
Clean up tags as typed: trim, drop the #, lower-case slug form, drop empties and duplicates, keep the order.
normalise_tags in RustTagged tags
3 capabilities
todo.parse-tags
Read a tags box as typed, "#Home, work errands", into normalised tags: split on spaces and commas.
parse_tags in Rust
todo.tag-counts
How many todos carry each tag, for a tag sidebar: most used first, open todos only unless asked.
tag_counts in Rust