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/handler/gemini_v1beta_handler.go

@@ -12,6 +12,7 @@ import (
 	"github.com/Wei-Shaw/sub2api/internal/pkg/antigravity"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/gemini"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/googleapi"
+	"github.com/Wei-Shaw/sub2api/internal/pkg/ip"
 	"github.com/Wei-Shaw/sub2api/internal/server/middleware"
 	"github.com/Wei-Shaw/sub2api/internal/service"
 
@@ -167,6 +168,9 @@ func (h *GatewayHandler) GeminiV1BetaModels(c *gin.Context) {
 	// 获取 User-Agent
 	userAgent := c.Request.UserAgent()
 
+	// 获取客户端 IP
+	clientIP := ip.GetClientIP(c)
+
 	// For Gemini native API, do not send Claude-style ping frames.
 	geminiConcurrency := NewConcurrencyHelper(h.concurrencyHelper.concurrencyService, SSEPingFormatNone, 0)
 
@@ -307,7 +311,7 @@ func (h *GatewayHandler) GeminiV1BetaModels(c *gin.Context) {
 		}
 
 		// 6) record usage async
-		go func(result *service.ForwardResult, usedAccount *service.Account, ua string) {
+		go func(result *service.ForwardResult, usedAccount *service.Account, ua string, cip string) {
 			ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 			defer cancel()
 			if err := h.gatewayService.RecordUsage(ctx, &service.RecordUsageInput{
@@ -317,10 +321,11 @@ func (h *GatewayHandler) GeminiV1BetaModels(c *gin.Context) {
 				Account:      usedAccount,
 				Subscription: subscription,
 				UserAgent:    ua,
+				IPAddress:    cip,
 			}); err != nil {
 				log.Printf("Record usage failed: %v", err)
 			}
-		}(result, account, userAgent)
+		}(result, account, userAgent, clientIP)
 		return
 	}
 }