Top 5 opportunities to reduce codebase size

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 :)

Measured the repo (jscpd 0.7% dup, knip 2 dead files, vulture 0, test audit 0): no massive cut left. Implemented the 5 largest real reductions (dead PlanPicker/PlanEndedBanner, check.sh Node probe, shared-store read helper, adapter hook partials; compat paths reported for owner decision). Quick gate green; PR #7530 queued to the merge lane.