refactor: Flatten directory structure

Move project files from uzdb/ subdirectory to root directory for cleaner project structure.

Changes:
- Move frontend/ to root
- Move internal/ to root
- Move build/ to root
- Move all config files (go.mod, wails.json, etc.) to root
- Remove redundant uzdb/ subdirectory nesting

Project structure is now:
├── frontend/        # React application
├── internal/        # Go backend
├── build/           # Wails build assets
├── doc/             # Design documentation
├── main.go          # Entry point
└── ...

🤖 Generated with Qoder

internal/middleware/logger.go

@@ -0,0 +1,98 @@
+package middleware
+
+import (
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+
+	"uzdb/internal/config"
+)
+
+// LoggerMiddleware returns a logging middleware using Zap
+func LoggerMiddleware() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		logger := config.GetLogger()
+		
+		// Start timer
+		start := time.Now()
+		
+		// Process request
+		c.Next()
+		
+		// Calculate duration
+		duration := time.Since(start)
+		
+		// Get client IP
+		clientIP := c.ClientIP()
+		
+		// Get method
+		method := c.Request.Method
+		
+		// Get path
+		path := c.Request.URL.Path
+		
+		// Get status code
+		statusCode := c.Writer.Status()
+		
+		// Get body size
+		bodySize := c.Writer.Size()
+		
+		// Determine log level based on status code
+		var level zapcore.Level
+		switch {
+		case statusCode >= 500:
+			level = zapcore.ErrorLevel
+		case statusCode >= 400:
+			level = zapcore.WarnLevel
+		default:
+			level = zapcore.InfoLevel
+		}
+		
+		// Create fields
+		fields := []zap.Field{
+			zap.Int("status", statusCode),
+			zap.String("method", method),
+			zap.String("path", path),
+			zap.String("ip", clientIP),
+			zap.Duration("duration", duration),
+			zap.Int("body_size", bodySize),
+		}
+		
+		// Add error message if any
+		if len(c.Errors) > 0 {
+			fields = append(fields, zap.String("error", c.Errors.String()))
+		}
+		
+		// Log the request
+		logger.Log(level, "HTTP request", fields...)
+	}
+}
+
+// RequestIDMiddleware adds a request ID to each request
+func RequestIDMiddleware() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		// Try to get request ID from header
+		requestID := c.GetHeader("X-Request-ID")
+		
+		// Generate if not present
+		if requestID == "" {
+			requestID = generateRequestID()
+		}
+		
+		// Set request ID in context
+		c.Set("request_id", requestID)
+		
+		// Add to response header
+		c.Header("X-Request-ID", requestID)
+		
+		c.Next()
+	}
+}
+
+// generateRequestID generates a simple request ID
+func generateRequestID() string {
+	return time.Now().Format("20060102150405") + "-" + 
+		time.Now().Format("000000.000000")[7:]
+}