Top 5 code reduction opportunities implementation

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 5 structural duplicates as single homes: ui/SaveRow (5 forms), e2e fixtures/measure.ts (8 specs), shared pytest fixtures (40 modules), routes/agents _saved tail, clock.as_utc None-aware. Net −93 lines (repo has ~0 textual duplication). Resumed prior attempt: fixed its red lint and 1 e2e. Quick gate + changed suites green; blind review PASS; visual check done, all 5 rows clean. PR #7450 queued to the merge lane. Memory: used mem-31277; proposed none.