feat: Add comprehensive backend validation, toast notifications, and Tokyo Night theme

- Backend: Add server-side validation with go-playground/validator/v10
- Frontend: Add toast notifications for API errors with @zerodevx/svelte-toast
- UI: Complete Tokyo Night theme redesign with modern animations
- Docs: Update COMPLETE_DOCUMENTATION.md and README.md with all enhancements
- Validation: Email format, password strength, and input sanitization
- UX: Real-time error feedback, loading states, and responsive design

bruno/auth/Login User.yml

@@ -0,0 +1,29 @@
+meta:
+  name: Login User
+  seq: 2
+http:
+  method: post
+  url: "{{base_url}}/api/auth/login"
+  body:
+    type: json
+    data: |
+      {
+        "login": "test@example.com",
+        "password": "password123"
+      }
+docs: |
+  ## Login User
+
+  Authenticates a user and returns a JWT token.
+
+  **Request Body:**
+  - `login` (string, required): Email address or username
+  - `password` (string, required): User's password
+
+  **Response:**
+  - `token` (string): JWT authentication token (24h expiry)
+  - `user` (object): User profile with id, email, username
+
+  **Error Responses:**
+  - 401: Invalid credentials
+  - 400: Invalid request data