fix(billing): 插件 HTTP 路由按操作拆路径 + 正确解析请求体

- 内核插件路由冲突仲裁按**路径**判重（不看 method），同一路径挂 4 个 method 会被
  当成 4 个插件抢同一路径 ⇒ 规则 API 不可用。拆成 /rules（GET）、/rules/replace
  （PUT）、/rules/add（POST）、/rules/remove（DELETE）。
- 插件 HTTP 分发交给 handler 的是**整个请求表**（body 是原始字符串），而直调导出
  拿到的是参数表；此前 PUT 把请求信封当成规则写进了 billing.json，规则全丢、价格表
  清空。新增 reqData() 统一解出 JSON 载荷。
- 生产复验：GET 返回 4 条规则；PUT 后 billing.json 保持规则形状；localzen（free）
  请求不计入 unpriced，codearts 未列价模型计入（预期收紧）。

(cherry picked from commit 79bc55cfbe)

internal/lua/plugins/billing.lua

@@ -346,6 +346,21 @@ do
   if not res then plugin.load_error = tostring(err) end
 end
 
+-- 插件 HTTP 分发把**整个请求表**交给 handler（method/path/body/headers…），
+-- body 是原始字符串；而直调导出（/call/...）拿到的就是参数表本身。这里统一
+-- 解出 JSON 载荷，避免"把请求信封当成规则写进 billing.json"（真实踩过：
+-- PUT 之后 billing.json 变成了整个请求的转储，规则全丢、价格表清空）。
+local function reqData(req)
+  if type(req) ~= "table" then return {} end
+  if type(req.json) == "table" then return req.json end
+  if type(req.body) == "string" and req.body ~= "" then
+    local ok, dec = pcall(json.decode, req.body)
+    if ok and type(dec) == "table" then return dec end
+  end
+  if req.method == nil and req.path == nil then return req end
+  return {}
+end
+
 -- ---- 规则编辑器的 HTTP 面（挂在插件自己的 /api/plugins/http/billing/ 下）----
 -- 规则属于插件，写盘也在插件内完成；内核没有 billing 端点。
 function plugin.__http_rules_get(req)
@@ -359,7 +374,7 @@ function plugin.__http_rules_get(req)
 end
 
 function plugin.__http_rules_put(req)
-  local body = (req and (req.json or req))
+  local body = reqData(req)
   if type(body) ~= "table" then
     return { status = 400, json = { error = "请求体必须是 JSON 对象" } }
   end
@@ -375,7 +390,7 @@ function plugin.__http_rules_put(req)
 end
 
 function plugin.__http_rules_add(req)
-  local body = (req and (req.json or req)) or {}
+  local body = reqData(req) or {}
   local copy = json.decode(json.encode(plugin.rules or { active = "", profiles = {} }))
   local target = nil
   for _, p in ipairs(copy.profiles or {}) do
@@ -407,7 +422,7 @@ function plugin.__http_rules_add(req)
 end
 
 function plugin.__http_rules_delete(req)
-  local body = (req and (req.json or req)) or {}
+  local body = reqData(req) or {}
   local copy = json.decode(json.encode(plugin.rules or { active = "", profiles = {} }))
   local target = nil
   for _, p in ipairs(copy.profiles or {}) do
@@ -448,14 +463,16 @@ function plugin.rules_put(args) return unwrap(plugin.__http_rules_put({ json = a
 function plugin.rules_add(args) return unwrap(plugin.__http_rules_add({ json = args or {} })) end
 function plugin.rules_delete(args) return unwrap(plugin.__http_rules_delete({ json = args or {} })) end
 
+-- 每条路由的 path 必须唯一：内核的路由冲突仲裁按**路径**（不看 method）判重，
+-- 同一路径挂 4 个 method 会被当成 4 个插件抢同一个路径。所以按操作拆路径。
 plugin.http = {
   { path = "billing/rules", method = "GET", handler = "__http_rules_get",
     roles = { "admin" }, description = "计费规则读取" },
-  { path = "billing/rules", method = "PUT", handler = "__http_rules_put",
+  { path = "billing/rules/replace", method = "PUT", handler = "__http_rules_put",
     roles = { "admin" }, description = "替换整份计费规则（插件自己写盘）" },
-  { path = "billing/rules", method = "POST", handler = "__http_rules_add",
+  { path = "billing/rules/add", method = "POST", handler = "__http_rules_add",
     roles = { "admin" }, description = "新增/替换一条计费规则" },
-  { path = "billing/rules", method = "DELETE", handler = "__http_rules_delete",
+  { path = "billing/rules/remove", method = "DELETE", handler = "__http_rules_delete",
     roles = { "admin" }, description = "删除一条计费规则" },
 }
 
@@ -1524,8 +1541,9 @@ plugin.ui = {
       return { "&": "&amp;", "<": "&lt;", ">": "&gt;", '"': "&quot;" }[c];
     });
   }
+  var OP_PATH = { GET: "", PUT: "/replace", POST: "/add", DELETE: "/remove" };
   function call(method, body) {
-    return fetch(API, {
+    return fetch(API + (OP_PATH[method] || ""), {
       method: method,
       credentials: "same-origin",
       headers: body ? { "Content-Type": "application/json" } : undefined,