Fix extraction markers interference in header comments

The example sed commands in the header contained the same
marker strings, causing extraction to capture header content.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

deck-frontend/deck-v4.2.html

@@ -16,9 +16,9 @@
 ║    - CSS: prefers-reduced-motion support                                     ║
 ║    - All v4.1 fixes included                                                 ║
 ║                                                                              ║
-║  EXTRACTION:                                                                 ║
-║    sed -n '/CSS_START/,/CSS_END/{//d;p}' deck.html > styles.css              ║
-║    sed -n '/JS_START/,/JS_END/{//d;p}' deck.html > app.js                    ║
+║  EXTRACTION (buscar marcadores en comentarios HTML):                         ║
+║    sed -n '/<!-- .* CSS_START/,/CSS_END .* -->/p' deck.html | ...            ║
+║    Ver README para comandos completos de extracción                          ║
 ║                                                                              ║
 ╚══════════════════════════════════════════════════════════════════════════════╝
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