paid-measurement-loop

# Paid Measurement Loop Reads a paid-ads change back against a control over a fixed readback window and returns Promote / Keep-testing / Rollback / Unproven. This is the paid readback loop — distinct from `roi-calculator` (the ROI/CPA math, which this delegates to) and `performance-analyzer` (cross-channel rollup); it owns the decision, the window, and the control. ## Quick Start ```text Read back the budget increase I made on Campaign X two weeks ago — did ROAS hold vs the control? I rotated in new creative on the prospecting set on the 10th — promote, keep testing, or roll back? Compare ROAS on my Meta vs Google search campaigns (I have both CSV exports) ``` ## Skill Contract **Expected output**: a per-change readback verdict (Promote / Keep-testing / Rollback / Unproven) with delta-vs-control on a primary metric (ROAS or CPA), the readback window used, normalization notes (attribution window + currency), and a handoff summary ready for `memory/paid-ads/paid-measurement-loop/`. - **Reads**: the change under test (what/when/owner), baseline vs candidate window exports (campaign report, GA4/ecommerce conversions), the control (unchanged campaign, sibling ad set, or holdout), target ROAS/CPA, attribution window per platform, and currency. - **Writes**: a user-facing readback table plus a reusable readback summary storable under `memory/paid-ads/paid-measurement-loop/`. - **Promotes**: confirmed Promote/Rollback decisions, the next-readback date, and any measurement-signa...