Rewrite NEXTGEN_INTEGRATOR.md from the early design draft into a full record: the diagnosis (our intensities are accurate and unbiased per ANODE, ~2x noisier than XDS), the experiment ledger of what worked and the many dead ends, the reusable tooling, and an honest assessment of the remaining gap. Fix the stale ProfileIntegrate2D.h header (it is wired and the default integrator, not a draft). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>