feat: Monthly token limits per user

Database:
- Add monthly_token_limit and token_limit_reset_day to users table
- Create ai_usage_monthly view for current month usage
- Add check_token_limit() function to verify available tokens
- Add get_user_usage_stats() function for historical usage

API Endpoints:
- PUT /admin/users/{user_id}/token-limit - Set monthly limit
- GET /admin/users/{user_id}/token-usage - Get user's current usage
- GET /admin/users/{user_id}/token-limit/check - Check if user has tokens

Features:
- Default limit: 100,000 tokens/month
- Reset day: 1st of month (configurable 1-28)
- Limit of 0 = unlimited tokens
- Enforce limits at API level (check before AI requests)

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

services/cms-service/src/main.rs

@@ -401,6 +401,18 @@ async fn main() {
             "/admin/ai-usage/global",
             get(handlers_admin::get_ai_usage_global),
         )
+        .route(
+            "/admin/users/{user_id}/token-limit",
+            put(handlers_admin::set_user_token_limit),
+        )
+        .route(
+            "/admin/users/{user_id}/token-usage",
+            get(handlers_admin::get_user_token_usage),
+        )
+        .route(
+            "/admin/users/{user_id}/token-limit/check",
+            get(handlers_admin::check_user_token_limit),
+        )
         .route_layer(middleware::from_fn(
             common::middleware::org_extractor_middleware,
         ));