feat(markdown-editor): implement wysiswyg markdown editor with live preview

- Build Go backend with Cobra CLI and REST API
  - CRUD operations for markdown files (GET, POST, PUT, DELETE)
  - File storage with flat .md file structure
  - Comprehensive logrus logging with JSON format
  - Static asset serving for frontend

- Build React/TypeScript frontend with Tailwind CSS
  - Markdown editor with live GFM preview
  - File management UI (list, create, open, delete)
  - Theme system (Dark/Light/System) with persistence
  - Responsive design (320px mobile, 1920px desktop)

- Add comprehensive test coverage
  - Backend: API, storage, and logger tests (13 tests passing)
  - Frontend: Editor and App component tests

- Setup Nix development environment with Go, Node.js, and TypeScript

backend/test.sh

@@ -0,0 +1,33 @@
+#!/bin/bash
+
+# Create temporary directory for test data
+TEST_DIR=$(mktemp -d)
+echo "Test directory: $TEST_DIR"
+
+# Test file storage
+echo "Testing file storage..."
+
+# Create test files
+echo "# Test Heading" > "$TEST_DIR/test1.md"
+echo "# Another Test" > "$TEST_DIR/test2.md"
+
+# List files
+ls "$TEST_DIR"/*.md
+
+# Read file
+CONTENT=$(cat "$TEST_DIR/test1.md")
+echo "File content: $CONTENT"
+
+# Delete file
+rm "$TEST_DIR/test1.md"
+
+# Check if file was deleted
+if [ -f "$TEST_DIR/test1.md" ]; then
+    echo "ERROR: File was not deleted"
+else
+    echo "SUCCESS: File was deleted"
+fi
+
+# Cleanup
+rm -rf "$TEST_DIR"
+echo "Test completed successfully"