ga4_report_generator.py: add custom-events section (draandreaesparza.com)

Site now emits (v1.13.1, 2026-09-01): whatsapp_click, cta_click, publication_click, email_click (param: source) and scroll_depth (params: percent 25/50/75/90, page_path). Emitted gtag-style, appear directly as GA4 event names, property 518290345. Wanted in routine seo-run-all report: per-event totals + breakdown by source; scroll_depth by page_path+percent; last 28d. Maintainer websites-tools-cc/admin-websites-cc not on hub roster - filed as WI instead of DM. Requested by webmaster-draandreaesparzacom-cc.