feat(auth): implement JWT authentication flow

This commit implements a full-stack authentication system using JWT.

On the backend, a new login endpoint `/api/token` is created. It
validates credentials and issues a signed JWT. A JWT middleware is added
to the server configuration to protect sensitive API endpoints like
`/api/category` and `/api/operation`. Configuration is now managed via a
`wallet.conf` file, loaded at startup.

On the frontend, this enables a complete authentication lifecycle: - A
new `/login` page allows users to enter their credentials. - A
`PrivateRoute` component wraps protected pages, redirecting
unauthenticated users to the login page. - API calls to protected
resources now include the `Authorization: Bearer <token>` header. - A
logout function is added to clear user session data.

refactor(ui): enhance history and category views

This commit also introduces major UI improvements.

The History modal has been completely redesigned. Operations are no
longer displayed as a flat list but are now grouped into tabs for Daily,
Weekly, Monthly, and Yearly views, providing a much clearer overview of
transactions.

The Categories modal now separates categories into "Incomes" and
"Expenses" tabs, reflecting the changes in the backend data model.

backend/api/Accessible.go

@@ -0,0 +1,17 @@
+package api
+
+import (
+	"github.com/gofiber/fiber/v2"
+	"github.com/golang-jwt/jwt"
+)
+
+func Accessible(c *fiber.Ctx) error {
+	return c.SendString("Accessible")
+}
+
+func Restricted(c *fiber.Ctx) error {
+	user := c.Locals("user").(*jwt.Token)
+	claims := user.Claims.(jwt.MapClaims)
+	name := claims["name"].(string)
+	return c.SendString("Welcome " + name)
+}

backend/api/Login.go

@@ -0,0 +1,36 @@
+package api
+
+import (
+	"backend/model"
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/gofiber/fiber/v2"
+	"github.com/golang-jwt/jwt"
+)
+
+func Login(c *fiber.Ctx) error {
+	var requestdata model.AuthRequest
+	err := c.BodyParser(&requestdata)
+	if err != nil {
+		return fmt.Errorf("Error parse body, %s", err)
+	}
+	if requestdata.Username != "tola" || requestdata.Password != "2808" {
+		return c.SendStatus(fiber.StatusUnauthorized)
+	}
+
+	claims := jwt.MapClaims{
+		"username":     "tola",
+		"is_superuser": true,
+		"exp":          time.Now().Add(time.Hour * 72).Unix(),
+	}
+
+	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
+
+	t, err := token.SignedString([]byte(os.Getenv("JWT_SECRET_KEY")))
+	if err != nil {
+		return c.SendStatus(fiber.StatusInternalServerError)
+	}
+	return c.JSON(fiber.Map{"token": t})
+}