refactor(ThreeSum): consolidate native execution proofs and controller families #2367

Implement the four concrete simplifications requested by the user after the native1.9992 theorem in #2358: consolidate the automatic ET controller, consolidate/factor the lower parameter/fixed-prime/callable families, prove ordinary time transfer once with a parameterized ET saving, and centralize repeated prefix-resource proof steps.

Owner/session: source-stack worker codex-root-3sum-simplify-20261103, branch work/three-sum-simplify-20261103 from c8c4faf. This is follow-up work; existing reviewed feature PRs and integration ownership are unchanged. Root owns production edits and mutable build outputs; bounded parallel scratch work owns runtime/prefix proposals only.

Acceptance: remove superseded implementations/interfaces and migrate every library/test/manual client without compatibility aliases; preserve native ordinary1.9992, all-length distinct-position correctness, actual computable code, charged work, dirty-memory/frame contracts, every-wide-width admission and polynomial prefix words/support. Preserve meaningful positive/negative/empty/threshold/dirty regression coverage and assess any changed finite-time interfaces explicitly. Measure actual net source reduction, including new shared infrastructure. Both manuals and selected-abstract impact must be covered; final affected checks, full validation and independent review are required. Publish reviewable focused commits/PRs and remove obsolete temporary worktrees.

AI assistance: OpenAI Codex implementation and separate independent agent review. The broader #1394 objective remains open through integration of the proved result; simplification does not replace that integration task.

State: awaiting maintainer integration in #2370. All four simplifications are implemented; final validation, independent review and the reviewed manual replay commit are recorded in that PR. The temporary source-only manual worktree has been removed; its pushed branch/commit and review evidence are preserved.