Reduce codebase by implementing top five refactoring

Identify top 5 opportunities to massively reduce the amount of code (lines of code) in any part of the repo: - Similar functionality that can be unified and reused - Code that has been valuable but no more - A front end component or a group of them duplicate another component/page functionality. Use the most modern and nice looking - etc. Now implement them :)

Repo already single-homed: no verbatim duplication outside vendor/. Shipped the 5 largest semantic folds (jaahd test git helper, api test fixtures, api slug/clock, web page-size + count formatter), net −90 lines; reverted 2 lanes that added lines. PR #7057 queued to merge lane; quick gate + 1467 api/944 jaahd/2316 web tests green. Visual check done (SES section clean). Criterion "massively" not satisfiable without removing features. Memory: none applied; proposed 0.