fix: use screen.width fallback in trackCustomEvent to prevent bot filter false positives

window.innerWidth is 0 in hidden/minimized tabs, causing the heuristic bot
scorer (added in #40) to drop legitimate custom events with a score of 5.
Use window.screen.width as fallback, matching the existing trackPageview logic.

public/script.js

@@ -320,7 +320,7 @@
       url: location.href,
       title: document.title,
       referrer: document.referrer || '',
-      screen: { width: window.innerWidth || 0, height: window.innerHeight || 0 },
+      screen: { width: window.innerWidth || window.screen.width, height: window.innerHeight || window.screen.height },
       session_id: getSessionId(),
       name: eventName.trim().toLowerCase(),
     };