cleanup: remove legacy insertr-cli and insertr-server directories

🧹 **Legacy Code Cleanup**

**Removed Directories:**
- `insertr-cli/` - 23 files removed (replaced by unified binary)
- `insertr-server/` - 24 files removed (replaced by unified binary)

**Updated References:**
- `TODO.md` - Updated file paths to reflect unified structure
- `scripts/dev.js` - Updated required/optional file checks

**Benefits:**
✅ **Single Source of Truth** - No more duplicate code or confusion
✅ **Smaller Repository** - Removed ~47 legacy files and binaries
✅ **Cleaner Development** - Only unified binary approach remains
✅ **Better Maintenance** - No legacy code paths to maintain

**All Functionality Preserved:**
- Database layer: `internal/db/`
- Content logic: `internal/content/`
- API handlers: `internal/api/`
- Commands: `cmd/enhance.go`, `cmd/serve.go`

The unified `insertr` binary now provides all functionality with enhanced architecture and no backwards compatibility baggage.

scripts/dev.js

@@ -43,13 +43,12 @@ const commands = {
         'demo-site/about.html', 
         'lib/dist/insertr.js',
         'lib/dist/insertr.min.js',
-        'insertr-server/cmd/server/main.go',
+        'cmd/serve.go',
         'package.json'
       ];
 
       const optionalFiles = [
-        'insertr-cli/insertr',
-        'insertr-server/insertr-server'
+        'insertr'
       ];
       
       let allGood = true;