fix(plugins): 出站主机授权两处真缺陷 —— 已启动 worker 看不到新授权、授权不落盘

生产实证：channels 插件的 auth/state 在主机已授权后仍被拒
（auth/state 失败: host "copilot.tencent.com" is not an allowed outbound destination），
而 /api/plugins/channels/kernel 明明显示 hosts_granted=26。

缺陷一（授权对已启动 worker 无效）：
  httpAllowlist 是不可变快照；bootPluginState 在 worker 启动时把指针绑进 Lua
  闭包，闭包与 worker 同寿。GrantExtraHosts 之后 ps.allowHTTP 被**整个换新**
  （newHTTPAllowlist 返回新实例），已启动的 worker 仍持旧指针 → 授权接口返回
  ok、设置页显示已批，请求却继续被拒。分片 VM（plugin_shard.go）同样中招。
  修法：allowlist 改为带 RWMutex 的**可变共享对象**，GrantExtraHosts 与
  rebuildOutboundAllowlistLocked 原地 add —— 所有闭包立即看到新授权，worker
  无需重建。rebuild 从"替换实例"改为"原地折叠"，并在注释里写明为什么。

缺陷二（授权不持久化）：
  .kernel-perms.json 只写 actions；hosts 授权只存在运行态 map，重启即失。
  设置页看不出异常（actions 有持久化，读起来像"都持久化了"）。
  修法：文件行改为 jsonPluginPolicy{actions,all_read,hosts}（旧文件向后兼容，
  纯 actions 行照常解析）；Load 恢复 extraHosts；Save 把每个插件的 host 授权
  与 actions 一起写入（支持"只批了主机、没批动作"的行）。

回归测试（internal/lua/plugin_http_test.go）：
- TestGrantExtraHostsVisibleToAlreadyBootedWorker：按事故顺序构造（先启动
  worker → 再授权），断言同一批 worker 立即可用新授权 + 旧引用不再失效。
- TestHostGrantsPersistAcrossRestart：授权落盘 + 新 registry 读回 + 插件重载
  后授权保留。

go test ./internal/lua/ 全绿；build/vet 通过。

internal/lua/plugin_http.go

@@ -43,6 +43,7 @@ import (
 	"net/http"
 	"net/url"
 	"strings"
+	"sync"
 	"time"
 
 	golua "github.com/aarzilli/golua/lua"
@@ -80,19 +81,39 @@ var httpClient = &http.Client{
 const httpGlobal = "__llmsproxy_http"
 
 // httpAllowlist is the set of hosts plugins may contact: the host of every
-// configured source's base_url.
+// configured source's base_url, plus every operator-granted extra host.
+//
+// It is a LIVE, shared object, not a snapshot. This matters: bootPluginState
+// binds one *httpAllowlist into every Lua closure at state-boot time, and those
+// closures live for the plugin's lifetime. Granting an extra host after a
+// worker booted must therefore MUTATE the same object the closures hold —
+// replacing ps.allowHTTP with a fresh instance would leave every already-booted
+// worker checking the STALE list, and a grant would look accepted (the API
+// answers ok, the UI shows it) while requests kept getting refused with
+// "not an allowed outbound destination". That exact failure shipped once.
+//
+// Mutations are rare (operator approves a host); lookups are per request.
 type httpAllowlist struct {
+	mu    sync.RWMutex
 	hosts map[string]bool
 }
 
 func newHTTPAllowlist(hosts []string) *httpAllowlist {
-	m := make(map[string]bool, len(hosts))
+	a := &httpAllowlist{hosts: make(map[string]bool, len(hosts))}
+	a.add(hosts)
+	return a
+}
+
+// add merges hosts into the live allowlist. Called by rebuild (source hosts
+// change on hot reload) and by GrantExtraHosts (operator approves a host).
+func (a *httpAllowlist) add(hosts []string) {
+	a.mu.Lock()
+	defer a.mu.Unlock()
 	for _, h := range hosts {
 		if h != "" {
-			m[strings.ToLower(h)] = true
+			a.hosts[strings.ToLower(h)] = true
 		}
 	}
-	return &httpAllowlist{hosts: m}
 }
 
 // allows reports whether host:port may be contacted. Ports 80/443 are implied
@@ -103,6 +124,8 @@ func (a *httpAllowlist) allows(host string, port string) bool {
 	if host == "" {
 		return false
 	}
+	a.mu.RLock()
+	defer a.mu.RUnlock()
 	if a.hosts[host] {
 		return true
 	}