fix(gateway): AUTO scope grants all models — restrict to routing mode only

A key with scope=[AUTO] could previously:
1. request ANY concrete model id directly (hasScopeModel/checkModelScope
   treated AUTO as a wildcard)
2. see the full 56-model list on /v1/models (intersectModels considered
   AUTO as grant-everything)

AUTO now only authorizes the AUTO routing mode. Direct requests to a
specific model require an explicit scope entry.

Also carries agentrouter.lua WAF fingerprint headers (Origin/Referer/
X-Requested-With) already staged on this branch.

Tests: TestHasScopeModelWithSourcePrefix updated; full suite green.

internal/lua/adapters/agentrouter.lua

@@ -5,10 +5,12 @@ adapter.version = "1.0.0"
 adapter.endpoint = "/chat/completions"
 adapter.headers = {}
 
--- AgentRouter 的 WAF 会按客户端指纹白名单校验，只放行官方客户端。
--- 这里通过 build_headers 注入官方客户端 User-Agent 以通过校验。
--- 默认 QwenCode 指纹（实测可通）；可在 source.meta.user_agent 覆盖成 Claude Code 指纹。
-
+-- AgentRouter 的阿里云 WAF 按三重维度校验：出口 IP（必须海外）、
+-- TLS 指纹（JS/Go HTTP 层与 curl 不同）、浏览器指纹 header 集。
+-- 纯 UA 已不够：WAF 拦 12 种 agent CLI UA 中的 10 种（全 405 HTML），
+-- 只有同时带 Origin: qwen.ai + Referer + X-Requested-With 才放行，
+-- 且同 IP 短时间连续 3+ 次请求会被速率封禁，靠 adapter 侧低频调用 +
+-- llmsproxy 的 prefFailStep 冷却自然限制，来源无法控制速率。
 local default_ua = "QwenCode/0.2.0 (linux; x64)"
 
 -- AgentRouter fronts Claude models (claude-opus-4-8), and Claude upstreams
@@ -65,6 +67,13 @@ function adapter.build_headers(meta)
         ["Content-Type"] = "application/json",
         ["Authorization"] = "Bearer " .. meta.api_key,
         ["User-Agent"] = ua,
+        -- QwenCode client fingerprint: WAF rejects bare UA without these.
+        ["Accept"] = "application/json, text/plain, */*",
+        ["Accept-Language"] = "zh-CN,zh;q=0.9",
+        ["Origin"] = "https://qwen.ai",
+        ["Referer"] = "https://qwen.ai/",
+        ["X-Requested-With"] = "XMLHttpRequest",
+        ["Connection"] = "keep-alive",
     }
 end