feat(api-key): 添加 IP 白名单/黑名单限制功能 (#221)

* feat(api-key): add IP whitelist/blacklist restriction and usage log IP tracking

- Add IP restriction feature for API keys (whitelist/blacklist with CIDR support)
- Add IP address logging to usage logs (admin-only visibility)
- Remove billing_type column from usage logs UI (redundant)
- Use generic "Access denied" error message for security

Backend:
- New ip package with IP/CIDR validation and matching utilities
- Database migrations for ip_whitelist, ip_blacklist (api_keys) and ip_address (usage_logs)
- Middleware IP restriction check after API key validation
- Input validation for IP/CIDR patterns on create/update

Frontend:
- API key form with enable toggle for IP restriction
- Shield icon indicator in table for keys with IP restriction
- Removed billing_type filter and column from usage views

* fix: update API contract tests for ip_whitelist/ip_blacklist fields

Add ip_whitelist and ip_blacklist fields to expected JSON responses
in API contract tests to match the new API key schema.

backend/internal/server/middleware/api_key_auth.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 
 	"github.com/Wei-Shaw/sub2api/internal/config"
+	"github.com/Wei-Shaw/sub2api/internal/pkg/ip"
 	"github.com/Wei-Shaw/sub2api/internal/service"
 
 	"github.com/gin-gonic/gin"
@@ -71,6 +72,17 @@ func apiKeyAuthWithSubscription(apiKeyService *service.APIKeyService, subscripti
 			return
 		}
 
+		// 检查 IP 限制（白名单/黑名单）
+		// 注意：错误信息故意模糊，避免暴露具体的 IP 限制机制
+		if len(apiKey.IPWhitelist) > 0 || len(apiKey.IPBlacklist) > 0 {
+			clientIP := ip.GetClientIP(c)
+			allowed, _ := ip.CheckIPRestriction(clientIP, apiKey.IPWhitelist, apiKey.IPBlacklist)
+			if !allowed {
+				AbortWithError(c, 403, "ACCESS_DENIED", "Access denied")
+				return
+			}
+		}
+
 		// 检查关联的用户
 		if apiKey.User == nil {
 			AbortWithError(c, 401, "USER_NOT_FOUND", "User associated with API key not found")