Gitignore-style exclusions globbing

Right now, the "manual exclusions" field in the `settings` table is just an array of exact paths. This is far from ideal because we often want to omit all files with a certain file name pattern or under a certain directory.

Basically... this is just what .gitignore-type files need to solve. So it would be nice to switch the exclusion specification to using something like a .gitignore format with e.g. globs and things.

Start by tracing how the manual exclusions field is read from the settings table and where exact-path matching is applied. Review the surrounding exclusion handling before deciding how .gitignore-style patterns, including globs and directory patterns, should behave; done means the configured exclusions support the requested pattern-based cases.

Written by the indexing model from the issue text.