feat: Rich text input with action and mention pills

- Implement RichChatInput component with visual pill rendering
- Add ActionPill component with blue circle icons for actions
- Add MentionPill component with blue diamond icons for files
- Support for /action and @filename pill creation
- Inline pill display in both input and message history
- Proper text selection, highlighting, and cursor positioning
- Backspace removal of entire pills
- Theme-aware styling for light/dark modes
- Consistent white pill backgrounds with blue accent icons
- Fixed line-breaking issues for natural text flow

Components added:
- RichChatInput.tsx: Main rich text input with pill rendering
- ActionPill.tsx: Blue circle pills for actions
- MentionPill.tsx: Blue diamond pills for file mentions
- MessageContent.tsx: Enhanced message display with pills

Features:
- Visual pills replace [Action] and @filename text
- Click and drag text selection works normally
- Double/triple click for word/all selection
- Pills flow inline with text content
- Proper cursor positioning and blinking
- Backspace removes entire pills as units

test_basic_functionality.py

@@ -0,0 +1,80 @@
+# Let's create a simple test to verify if the basic text replacement is working
+print("🧪 Testing Basic Text Replacement")
+print("=" * 50)
+
+# Read the handleActionSelect function
+with open('ui/desktop/src/components/ChatInput.tsx', 'r') as f:
+    content = f.read()
+
+# Check if the function exists and has the right structure
+if 'handleActionSelect' in content:
+    print("✅ handleActionSelect function found")
+    
+    # Check for key components
+    if 'setDisplayValue(newValue)' in content:
+        print("✅ setDisplayValue call found")
+    if 'setValue(newValue)' in content:
+        print("✅ setValue call found")
+    if 'actionInfo.label' in content:
+        print("✅ actionInfo.label usage found")
+    if 'lastSlashIndex' in content:
+        print("✅ slash detection logic found")
+    
+    # Extract the function for analysis
+    start = content.find('const handleActionSelect = (actionId: string) => {')
+    if start != -1:
+        # Find the end of the function
+        brace_count = 0
+        pos = start
+        while pos < len(content):
+            if content[pos] == '{':
+                brace_count += 1
+            elif content[pos] == '}':
+                brace_count -= 1
+                if brace_count == 0:
+                    end = pos + 1
+                    break
+            pos += 1
+        
+        function_code = content[start:end]
+        print(f"\n📝 Function length: {len(function_code)} characters")
+        
+        # Check for potential issues
+        if 'cursorPosition = 0' in function_code:
+            print("⚠️  WARNING: cursorPosition hardcoded to 0")
+        if 'actionPopover.cursorPosition' in function_code:
+            print("✅ Using actionPopover.cursorPosition")
+        if 'console.log' in function_code:
+            print("✅ Debug logging present")
+            
+else:
+    print("❌ handleActionSelect function not found")
+
+print("\n🔍 Checking RichChatInput integration...")
+
+# Check RichChatInput
+with open('ui/desktop/src/components/RichChatInput.tsx', 'r') as f:
+    rich_content = f.read()
+
+if 'actionRegex = /\\[([^\\]]+)\\]/g' in rich_content:
+    print("✅ Action regex pattern found")
+if 'ActionPill' in rich_content:
+    print("✅ ActionPill component imported")
+if 'renderContent' in rich_content:
+    print("✅ renderContent function found")
+
+print("\n🎯 Next Steps:")
+print("1. Open browser dev tools")
+print("2. Type '/' in chat input")
+print("3. Click an action")
+print("4. Look for these console messages:")
+print("   - 🎯 ActionPopover: handleItemClick called")
+print("   - 🎯 handleActionSelect called with:")
+print("   - 📍 Current state:")
+print("   - 🔄 Text replacement:")
+print("   - 🎨 RichChatInput renderContent called")
+
+print("\n💡 If no console logs appear:")
+print("- ActionPopover might not be calling onSelect")
+print("- handleActionSelect might not be connected")
+print("- Check for JavaScript errors in console")