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 :)

No PR: nine prior cuts (12891–13087) left the tree at its floor. jscpd, vulture, knip, an AST import graph and a normalised near-dup scan over ~1.5M lines found 0 dead modules/functions/symbols and no clone beyond signatures. Deferred: OpenAPI-generated types.ts (ADR-level).