feat: major update - Markdown Editor, CodeMirror upgrades, SEO improvements, tool cleanup

- Added new Markdown Editor with live preview, GFM support, PDF/HTML/DOCX export
- Upgraded all paste fields to CodeMirror with syntax highlighting and expand/collapse
- Enhanced Object Editor with advanced URL fetching and preview mode
- Improved export views with syntax highlighting in Table/Object editors
- Implemented SEO improvements (FAQ schema, breadcrumbs, internal linking)
- Added Related Tools recommendations component
- Created custom 404 page with tool suggestions
- Consolidated tools: removed JSON, Serialize, CSV-JSON (merged into main editors)
- Updated documentation and cleaned up redundant files
- Updated release notes with user-centric improvements

src/components/MobileAdBanner.js

@@ -0,0 +1,66 @@
+import React, { useEffect, useState } from 'react';
+import { X } from 'lucide-react';
+
+/**
+ * MobileAdBanner Component - Sticky bottom banner for mobile
+ * Visible only on mobile/tablet, hidden on desktop
+ * Includes close button for better UX
+ */
+const MobileAdBanner = ({ slot = 'REPLACE_WITH_MOBILE_SLOT' }) => {
+  const [visible, setVisible] = useState(true);
+  const [closed, setClosed] = useState(false);
+
+  useEffect(() => {
+    // Check if user previously closed the banner (session storage)
+    const wasClosed = sessionStorage.getItem('mobileAdClosed');
+    if (wasClosed === 'true') {
+      setClosed(true);
+      setVisible(false);
+    }
+  }, []);
+
+  useEffect(() => {
+    if (visible && !closed) {
+      try {
+        (window.adsbygoogle = window.adsbygoogle || []).push({});
+      } catch (e) {
+        console.error('AdSense error:', e);
+      }
+    }
+  }, [visible, closed]);
+
+  const handleClose = () => {
+    setVisible(false);
+    setClosed(true);
+    sessionStorage.setItem('mobileAdClosed', 'true');
+  };
+
+  if (!visible || closed) return null;
+
+  return (
+    <div className="xl:hidden fixed bottom-0 left-0 right-0 z-50 bg-white dark:bg-gray-900 shadow-lg border-t border-gray-200 dark:border-gray-700">
+      <button
+        onClick={handleClose}
+        className="absolute top-1 right-1 p-1 text-gray-500 hover:text-gray-700 dark:text-gray-400 dark:hover:text-gray-200 bg-white dark:bg-gray-800 rounded-full shadow-sm"
+        aria-label="Close ad"
+      >
+        <X className="h-4 w-4" />
+      </button>
+      <div className="flex justify-center py-2">
+        <ins
+          className="adsbygoogle"
+          style={{ 
+            display: 'inline-block', 
+            width: '320px', 
+            height: '50px' 
+          }}
+          data-ad-client="ca-pub-8644544686212757"
+          data-ad-slot={slot}
+          data-ad-format="fixed"
+        />
+      </div>
+    </div>
+  );
+};
+
+export default MobileAdBanner;