feat(plugins): ccquota 多账户额度插件 + 页面→Lua 调用通道

A quota plugin cannot work on billing's model. Billing reports what the gateway
already measured, delivered on hooks during request forwarding. A plan balance
has no such arrival path: it exists only on the vendor's side, and the only way
to learn it is to ask — at the moment the operator clicks Refresh. No hook fires
on a click, and pluginAPI offered only state read/write.

So this adds the missing piece: POST /api/plugins/{name}/call/{fn}, plus
pluginAPI.call on the page side.

## Why the gate is an explicit export list

That endpoint is an HTTP surface into a Lua state. Without a declared allowlist
it would let any caller invoke the plugin's private helpers with crafted
arguments and read whatever it can see — for a plugin holding an API key, that
is handing the key to anyone who can POST. So a function is callable only if the
plugin listed it in plugin.exports. A plugin with no exports has no callable
surface; reading the missing list as "allow all" is exactly the failure mode
worth designing against. The endpoint is also admin-only.

## ccquota

One account per configured source on api.commandcode.ai, keyed by that source's
own key — two keys on one host are two seats, and both are shown. Reads
/alpha/whoami, /alpha/billing/credits, /alpha/billing/subscriptions and
/alpha/usage/summary. Each endpoint degrades independently: a vendor retiring
one route must not blank the others, and a key out of quota still reads credits
fine while inference 401s, so the report records WHICH part failed rather than
rendering a zero that reads as "no quota left".

The 401-is-everything trap: those endpoints need a bearer token plus three
headers. The token lives in the table now, per request. Passing the shared
header table straight through — my first version — yields 401 on every
endpoint, which is indistinguishable from a revoked key and sent me auditing the
account instead of the plugin.

## Also fixed: three real defects found by going live

- The bridge was registered as `httpGlobal` (the Go const's IDENTIFIER) instead
  of `__llmsproxy_http` (its VALUE). Green unit tests, "attempt to call global
  '__llmsproxy_http' (a nil value)" on first real request. Now a test boots a
  real plugin and calls it the way a plugin does.
- The call router kept `call/` in the function name, so every call 502'd with
  `does not export "call/collect_account"` while the exports list looked fine.
- readPluginExports used luaToJSON, which needs the `json` global — not yet
  installed while a plugin is registering — so it silently returned an empty
  list and every export looked undeclared. It uses luaTableToGoValue now.

Two tests hardcoded counts ("1 bundled plugin", "4 pages") and turned red the
moment a second bundled plugin existed. They now assert what they mean: billing
is among the bundled plugins, and the pages this test contributed all merged in
order. A count assertion is a changelog detector.

## Verified on production

  commandcode    2198972886@qq.com  active  $0.0811  5h 0/14  wk 0.803/35  44,921 req
  commmandcode2  jianf3112@gmail.com active  $0.0700  5h 0/14  wk 0/35      43,827 req

Co-Authored-By: ModelRouter <noreply@modelrouter.dev>
(cherry picked from commit 111dc6d53f)
(cherry picked from commit 22c9215b02)

internal/gateway/ui/index.html

@@ -5570,6 +5570,28 @@ toast(t("kAutoChainGlobal"));
           if (!r.ok) throw new Error((await r.json().catch(() => ({}))).error?.message || r.status);
           return true;
         },
+        // call invokes one of the plugin's OWN exported functions. Billing never
+        // needs this — its numbers arrive on hooks while the gateway forwards a
+        // request — but a plugin that must do work on demand (asking a vendor
+        // for a balance when the operator clicks Refresh) has no other way to
+        // reach its own code: no hook fires on a click.
+        //
+        // Admin-only server side, and the plugin must have listed the function in
+        // plugin.exports, so this cannot be used to reach a plugin's internals.
+        async call(name, fn, args) {
+          const r = await fetch(
+            "/api/plugins/" + encodeURIComponent(name) + "/call/" + encodeURIComponent(fn),
+            {
+              method: "POST",
+              credentials: "same-origin",
+              headers: { "Content-Type": "application/json" },
+              body: JSON.stringify(args || {}),
+            },
+          );
+          const body = await r.json().catch(() => ({}));
+          if (!r.ok) throw new Error(body.error?.message || r.status);
+          return body.result;
+        },
         onTabShown(fn) {
           PLUGIN_TAB_CBS.__last = PLUGIN_TAB_CBS.__last || [];
           PLUGIN_TAB_CBS.__last.push(fn);