Implement JWT authentication and app passkey support

- Add JWT token generation and validation
- Implement bcrypt password hashing
- Create auth service with register/login/refresh/logout
- Add app passkey generation and management
- Implement protected routes and auth middleware
- Add comprehensive tests for new functionality

internal/middleware/auth.go

@@ -0,0 +1,52 @@
+package middleware
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+
+	"github.com/dhao2001/mygo/internal/api"
+	"github.com/dhao2001/mygo/internal/auth"
+)
+
+const userIDKey = "user_id"
+
+// AuthRequired returns a Gin middleware that validates JWT access tokens.
+// On success, it injects the user ID into the context via c.Get("user_id").
+func AuthRequired(jwtSecret []byte) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		header := c.GetHeader("Authorization")
+		if header == "" {
+			api.Error(c, http.StatusUnauthorized, "missing authorization header")
+			c.Abort()
+			return
+		}
+
+		parts := strings.SplitN(header, " ", 2)
+		if len(parts) != 2 || !strings.EqualFold(parts[0], "bearer") {
+			api.Error(c, http.StatusUnauthorized, "invalid authorization header format")
+			c.Abort()
+			return
+		}
+
+		claims, err := auth.ParseToken(parts[1], jwtSecret)
+		if err != nil {
+			api.Error(c, http.StatusUnauthorized, "invalid or expired token")
+			c.Abort()
+			return
+		}
+
+		c.Set(userIDKey, claims.UserID)
+		c.Next()
+	}
+}
+
+// GetUserID extracts the user ID injected by AuthRequired.
+func GetUserID(c *gin.Context) string {
+	v, _ := c.Get(userIDKey)
+	if v == nil {
+		return ""
+	}
+	return v.(string)
+}