Implement Top 5 Code Reduction Opportunities

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 (0.2% product duplication, no dead surface) then shipped the 5 largest remaining cuts: ORM PK/stamp mixins (−116), one keyset cursor codec, shared useTaskActions, single-homed vocabularies/formatters, one tracked-files query; ~−165 net, schema unchanged. Full gate green twice, blind review+security+verifier pass, PR #5480 merged 8a41790c1, Jaah Deploy success. Visual check: board and Efficiency tab rendered clean. Assumed "massive" = largest honest cuts. Deferred: TaskPane→FeedList port (~300), hosts/nodes roster cursors onto keyset, 4 console UX items (task_create refused 403 for coder). mem-15536 held.