🔧 Fix CORS and API endpoint issues

- Fix API endpoint paths (remove trailing slashes for 405 errors)
- Update API URLs to use api-todo.hyungi.net subdomain for HTTPS compatibility
- Improve CORS settings parsing in backend (handle brackets and quotes)
- Add frontend volume mount to docker-compose for real-time file updates
- Update Synology deployment config with wildcard CORS settings

Resolves:
- 405 Method Not Allowed errors
- Mixed Content security issues (HTTPS → HTTP)
- CORS preflight request failures
- Docker build requirements for every file change

Tested: API endpoints now correctly use HTTPS subdomain, eliminating security blocks

frontend/static/js/api.js

@@ -3,9 +3,15 @@
  */
 
 // 환경에 따른 API URL 설정
-const API_BASE_URL = window.location.hostname === 'localhost' 
+const API_BASE_URL = window.location.hostname === 'localhost' || window.location.hostname === '127.0.0.1'
     ? 'http://localhost:9000/api'  // 로컬 개발 환경
-    : `${window.location.protocol}//${window.location.hostname}:9000/api`;  // 시놀로지 배포 환경
+    : window.location.hostname === 'todo.hyungi.net'
+        ? 'https://api-todo.hyungi.net/api'  // API 서브도메인 (HTTPS 통일)
+        : window.location.hostname === '192.168.219.116'
+        ? 'http://192.168.219.116:9000/api'  // IP 직접 접근
+        : window.location.protocol === 'https:'
+            ? `https://${window.location.hostname}:9000/api`  // HTTPS 환경
+            : `http://${window.location.hostname}:9000/api`;   // HTTP 환경
 
 class ApiClient {
     constructor() {
@@ -161,7 +167,7 @@ const AuthAPI = {
 // Todo 관련 API
 const TodoAPI = {
     async getTodos(status = null, category = null) {
-        let url = '/todos/';
+        let url = '/todos/';  // 슬래시 추가
         const params = new URLSearchParams();
         
         if (status && status !== 'all') params.append('status', status);
@@ -175,27 +181,27 @@ const TodoAPI = {
     },
 
     async createTodo(todoData) {
-        return api.post('/todos/', todoData);
+        return api.post('/todos/', todoData);  // 슬래시 추가
     },
 
     async updateTodo(id, todoData) {
-        return api.put(`/todos/${id}/`, todoData);
+        return api.put(`/todos/${id}`, todoData);
     },
 
     async deleteTodo(id) {
-        return api.delete(`/todos/${id}/`);
+        return api.delete(`/todos/${id}`);
     },
 
     async completeTodo(id) {
-        return api.put(`/todos/${id}/`, { status: 'completed' });
+        return api.put(`/todos/${id}`, { status: 'completed' });
     },
 
     async getTodayTodos() {
-        return api.get('/calendar/today/');
+        return api.get('/calendar/today');
     },
 
     async getTodoById(id) {
-        return api.get(`/todos/${id}/`);
+        return api.get(`/todos/${id}`);
     },
 
     async uploadImage(imageFile) {