Revert "feat: add HTML report screenshot generation via Playwright"

This reverts commit f370caeff9.

rotation/backtest_viewer.html

@@ -152,15 +152,11 @@ tr.below-threshold { color: #484f58; }
 </div>
 
 <script>
-// Use window. to allow external access (for Playwright screenshot injection)
-window.DATA = null;
-window.currentIdx = 0;
-window.playing = false;
-window.playTimer = null;
-window.rebalanceDays = [];
-
-// Convenience aliases for script-internal use
-const DATA_PROXY = { get data() { return window.DATA; }, set data(v) { window.DATA = v; } };
+let DATA = null;
+let currentIdx = 0;
+let playing = false;
+let playTimer = null;
+let rebalanceDays = [];
 
 const $ = id => document.getElementById(id);