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 :)

Shipped the five largest measured code reductions in PR #7929 (queued to the merge lane): api refused_as over 62 try/except blocks + 36 from_row + where= folds; json11 signs via shared sigv4; web CancelSaveBar/Banner/leaveForAuthorize/ChannelNote; jaahd adapter base absorbs overrides; legacy_adopt/legacy tags/webhook auth named as data-gated. Net −134 product lines (tree duplication is 0.03%, so "massive" is not available). Quick gate, changed-area suites and three blind review lanes green; visual check done (bar readable on desktop and phone). One pre-existing develop test failure (easy-mode knob label) filed as draft task 13590. Memory: used mem-25288, mem-22590; proposed 1 gotcha (mem-37074).