Identify and implement top five code reduction

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 the top five code-reduction folds (-817 net lines over 146 files: shared jaahd test fakes, shared API fixtures + parametrized tests, web helper folds, one SQS drain + storage base, daemon MarkerChannel/run_capped/LoginAdapterBase). Resume re-verified the prior diff, took 4 review fixes, restored 3 compliance exports a rebase made live. Quick gate + suites green; PR #6934 merged by the lane (c1ee6b18). Visual check done: all surfaces render as before.