feat(quota): OpenDesign 出站主机加入白名单

插件出站白名单 = 已配置源的 host。这条规则对每个 adapter 都成立，直到
OpenDesign —— 它把推理和计费拆在两个域上：推理 amr-link，计费 amr-api。
adapter 从推理主机推导计费主机，于是它请求的 host 从来不是操作员配过的
那个，请求在离开进程前就被拒，报"不是允许的出站目标"，读起来像插件 bug。

core.sourceHosts 现在同时加入派生主机，且仅当源本身就在 amr-link 上
（没有 OpenDesign 源的部署不会凭空获得这条授权）。

派生规则前后端各存一份，因为 Go 建白名单、Lua 建 URL，两边不一致的表现是
「请求被拒」而不是「命名不匹配的错误」。规则改成了完整主机名匹配：
`amr-link.` 前缀写法会把 amr-link.example.com 也改写成 OpenDesign 地址。

顺带修掉一个真缺陷：Lua 侧先 `gsub("/+$")` 再匹配主机名，而 base_url 是
`https://amr-link.open-design.ai/v1` —— 带路径时整串拿去匹配 `^...$`
永远不命中，改写静默失效，探测打到推理主机。改成先切路径。

这个缺陷是「行为断言」抓到的：上一版判据 grep 源码里的 gsub 模式，而
gsub 模式在改前改后都"看起来对"。8/8 变异全杀。

internal/core/core.go

@@ -650,11 +650,29 @@ func (c *Core) rebuildRegistry() error {
 // allowlist for plugin outbound HTTP. Unparseable URLs are skipped rather than
 // failing startup: a malformed base_url is already rejected when the provider is
 // built, and it must not take plugins down with it.
+//
+// A source may also imply a SECOND host. OpenDesign splits inference
+// (amr-link.open-design.ai) from billing (amr-api.open-design.ai), and the
+// quota plugin derives the billing host from the inference one — so the host it
+// asks for is not the host the operator configured, and the request would be
+// refused with a message that reads like a plugin defect. Adding the derived
+// host here is what makes the probe reachable.
+//
+// The grant stays scoped: only a source that IS on amr-link pulls in amr-api, so
+// a deployment with no OpenDesign source does not silently gain the entry.
 func sourceHosts(cfg *config.Config) []string {
 	if cfg == nil {
 		return nil
 	}
 	out := make([]string, 0, len(cfg.Sources))
+	seen := make(map[string]bool, len(cfg.Sources))
+	add := func(h string) {
+		if h == "" || seen[h] {
+			return
+		}
+		seen[h] = true
+		out = append(out, h)
+	}
 	for _, s := range cfg.Sources {
 		if s.BaseURL == "" {
 			continue
@@ -663,11 +681,27 @@ func sourceHosts(cfg *config.Config) []string {
 		if err != nil || u.Hostname() == "" {
 			continue
 		}
-		out = append(out, u.Hostname())
+		add(u.Hostname())
+		add(deriveBillingHost(u.Hostname()))
 	}
 	return out
 }
 
+// deriveBillingHost returns the billing host a configured source implies, or
+// the host unchanged when it implies none.
+//
+// Kept in Go as well as in the Lua adapter because the two must agree: Go builds
+// the allowlist and Lua builds the request URL, and a disagreement shows up as a
+// refused request rather than as an error naming the mismatch. The rule is the
+// full hostname, not a prefix — `amr-link.` as a prefix would also rewrite
+// amr-link.example.com into an OpenDesign address.
+func deriveBillingHost(host string) string {
+	if host == "amr-link.open-design.ai" {
+		return "amr-api.open-design.ai"
+	}
+	return host
+}
+
 // buildAutoChain rebuilds the AUTO chain snapshot from config.yaml rules
 // against the current providers. Slot model ids are normalized to the exact
 // configured spelling (case-insensitive match), otherwise ModelFor would fall