Implement Top Five Codebase 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 :)

Implemented the top five ungated cuts (net −258 lines, 51 files): API _or_404/cursor/slug twins onto their homes; dead product functions out; one jaahd session-tree walker; tools/jaahd atomic-write and dotenv twins; web wrappers and dead exports. ./dc check full green; blind code+security+verifier lanes pass; PR #5483 merged, Jaah Deploy success. Not massive by design: the SKYNET aliases, NodeLink v1 wire, _legacy_* columns and TaskPane/FeedList stay gated on fleet facts or a migration (deferred, named in the report). Visual check done on the live slot: host detail and tasks board clean at 1280/390 px. UI suggestions (Machines tab strip truncation, host not-found action) are deferred follow-ups since task creation is unlicensed for coder. Memory: relied on mem-16764, mem-16980, mem-17767, mem-5120, mem-5787; proposed mem-17791.