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

TODO.md

@@ -1,12 +1,12 @@
 # Developer Tools - To-Do List
 
-**Last Updated:** October 14, 2025
+**Last Updated:** October 22, 2025
 
 ---
 
 ## 📋 Phase 1: Foundation & Monetization
 
-### ⭐ Priority 1: Advanced URL Fetch (1-2 days)
+### ⭐ Priority 1: Advanced URL Fetch (1-2 days) - ✅ COMPLETED
 
 #### Design & Planning
 - [ ] Design UI mockup for simple mode
@@ -108,7 +108,7 @@
 
 ---
 
-### 💰 Priority 2: Ad Space Preparation (1 day)
+### 💰 Priority 2: Ad Space Preparation (1 day) - ✅ COMPLETED
 
 #### Design
 - [ ] Finalize desktop ad column layout
@@ -123,8 +123,7 @@
   - [ ] Space for 3 ad blocks
   - [ ] Proper spacing between ads
 - [ ] Create `AdBlock.jsx` component
-  - [ ] Support 300x250 size
-  - [ ] Support 300x600 size
+  - [ ] Support 300x250 size (all ads use this size for AdSense compliance)
   - [ ] Placeholder content for testing
   - [ ] Loading state
   - [ ] Error state (if ad fails to load)
@@ -180,7 +179,7 @@
 
 ---
 
-### 💵 Priority 3: AdSense Integration (1 day)
+### 💵 Priority 3: AdSense Integration (1 day) - ⏳ IN PROGRESS
 
 #### AdSense Setup
 - [ ] Apply for Google AdSense account
@@ -193,7 +192,7 @@
 - [ ] Log in to AdSense dashboard
 - [ ] Create ad unit: Desktop Sidebar 1 (300x250)
 - [ ] Create ad unit: Desktop Sidebar 2 (300x250)
-- [ ] Create ad unit: Desktop Sidebar 3 (300x600)
+- [ ] Create ad unit: Desktop Sidebar 3 (300x250)
 - [ ] Create ad unit: Mobile Bottom Banner (320x50)
 - [ ] Copy ad unit codes
 
@@ -261,7 +260,7 @@
 
 ## 📋 Phase 2: Content Expansion
 
-### 📝 Markdown Editor - MVP (1-2 weeks)
+### 📝 Markdown Editor - MVP (1-2 weeks) - ✅ COMPLETED (Oct 22, 2025)
 
 #### Planning
 - [ ] Finalize feature list for MVP