Reduce repository code through refactoring and consolidation

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 :)

Top-5 code-reduction opportunities implemented and merged as PR #6941 (113 files, +666/−2125 = −1,459): retired applied one-shot migration tests, consolidated web test fixtures, single-homed API and web helpers, swapped raw MUI for ui/ primitives. Quick gate 582/582 green; three review lanes pass; visual check done (guard filters clean at desktop and 390px); Jaah Deploy of merge cc728ea6c succeeded. Larger reductions (migration-chain collapse, skynet alias retirement, vendor/yaml) are gated and named as deferred follow-ups. Memory: used mem-25288, mem-25697, mem-23434; proposed 0.