fix(startup): 密钥警告改读真实生效的 key 集合

启动时那条「gateway_keys is EMPTY — without a key every request is rejected」
读的是 legacy 的 cfg.GatewayKeys 段，而鉴权实际用 cfg.Keys（core.ListKeys）。
seedKeys 首次启动把 gateway_keys 搬进 keys[] 之后，YAML 里那个列表就不再
被鉴权使用。于是在它被清空（例如轮换掉 starter key 之后）而 keys[] 仍有
7 把可用 key（含 admin）时，进程每次启动都谎报「所有请求都会被拒绝」。

实测：生产日志出现该警告，而同一个 key 请求 /v1/models 返回 200。

- main.go 改为检查 c.ListKeys()，文案改成不绑定字段名。
- 顺带删掉 gateway.New 的 gatewayKeys 参数：函数体从未使用它，
  只读 ListKeys()，留着会继续诱导人以为鉴权来自那个列表。

判据：e2e/TestStartupWarningReflectsRealKeysNotLegacyList —— 构造
「gateway_keys 空 + keys[] 有 key」的真实形态，先断言该 key 确实能鉴权，
再断言日志里不再出现那句谎报。变异验证：回退成 GatewayKeys() 即变红。

cmd/llmsproxy/main.go

@@ -73,19 +73,26 @@ func main() {
 		}
 	}
 
-	gw, err := gateway.New(c, c.GatewayKeys())
+	gw, err := gateway.New(c)
 	if err != nil {
 		log.Fatalf("[llmsproxy] gateway: %v", err)
 	}
 
 	// Ops hygiene: surface the two most common footguns instead of silently
 	// running with them.
-	if keys := c.GatewayKeys(); len(keys) == 0 {
-		log.Printf("[llmsproxy] WARNING: gateway_keys is EMPTY — without a key every request is rejected")
+	//
+	// Read the AUTHORITATIVE source. Auth uses core.ListKeys() (cfg.Keys), not
+	// the legacy cfg.GatewayKeys list: seedKeys copies gateway_keys into keys[]
+	// on first start and the YAML list is ignored for auth afterwards. Checking
+	// GatewayKeys() here made the warning lie — once the legacy list was empty
+	// (e.g. after rotating the starter key away) it reported "every request is
+	// rejected" while seven working keys, one of them admin, were in service.
+	if keys := c.ListKeys(); len(keys) == 0 {
+		log.Printf("[llmsproxy] WARNING: no gateway key configured — every request will be rejected. Add one in the WebUI or set gateway_keys")
 	} else {
 		for _, k := range keys {
-			if k == "sk-gw-local-0001" || k == "sk-local-0001" {
-				log.Printf("[llmsproxy] WARNING: gateway key %q looks like the starter/example key — rotate it before exposing the gateway", k)
+			if k.Key == "sk-gw-local-0001" || k.Key == "sk-local-0001" {
+				log.Printf("[llmsproxy] WARNING: gateway key %q looks like the starter/example key — rotate it before exposing the gateway", k.Key)
 			}
 		}
 	}