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 :)

Implemented five semantic unifications (ui/SelectFilters, shared artifact/attachment viewer pieces, GHA runners list on FeedList, EFS picker reset rules, test clone folds): 31 files, −749 lines net. Quick gate, changed suites, blind review and verifier lanes green; visual check done on live stack at 1440/390px. PR #7494 queued to the merge lane. Deferred: no safely removable legacy code found; large levers (legacy CLI runtime, identity dual-write contraction) need an operator decision or a migration.