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/lua/plugin_http_test.go

@@ -148,4 +148,70 @@ func TestPluginHTTPErrorPathIsPairNotRaise(t *testing.T) {
 	if _, err := readHTTPRequestSpec(L); err == nil {
 		t.Fatal("a missing argument table must be an error, not a panic")
 	}
-}
+}
+// The bridge must be reachable under the name plugins actually call.
+//
+// This exists because the registration once used the CONSTANT'S IDENTIFIER as
+// the Lua global name (`registerFn(L, "httpGlobal", …)`) rather than its VALUE,
+// so the bridge was published as `httpGlobal` while every plugin called
+// `__llmsproxy_http`. The failure only appeared at runtime, as
+// "attempt to call global '__llmsproxy_http' (a nil value)" on the first real
+// request — after the unit tests were green, because they drove the Go-side
+// helpers directly and never went through Lua name resolution.
+//
+// So this test boots a real plugin and calls the bridge the way a plugin does.
+func TestPluginHTTPBridgeIsReachableUnderItsLuaName(t *testing.T) {
+	dir := t.TempDir()
+	ps := NewPlugins(NewVM(dir), dir)
+	ps.SetOutboundHosts([]string{"127.0.0.1"})
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"credits":{"monthlyCredits":1.5}}`))
+	}))
+	defer srv.Close()
+
+	// The plugin asks for a loopback URL, which is allowed without being
+	// configured as a source. It type-checks both the table and arg.url, so a
+	// malformed call is reported by the plugin rather than as a bewildering URL
+	// parse error from the bridge.
+	src := `
+local P = {}
+P.name = "httpprobe"
+P.version = "1.0.0"
+P.exports = { "probe" }
+-- Call passes the WHOLE argument table as a single Lua argument, which is the
+-- same convention the hooks use and what a plugin page's pluginAPI.call ends up
+-- producing. Taking the table (not a bare string) is the correct shape.
+function P.probe(arg)
+  if type(arg) ~= "table" then return { error = "probe takes the args table, got " .. type(arg) } end
+  if type(arg.url) ~= "string" then return { error = "arg.url must be a string, got " .. type(arg.url) } end
+  local res, err = ` + httpGlobal + `({ url = arg.url, method = "GET" })
+  if res == nil then return { error = tostring(err) } end
+  return { status = res.status, body = res.body }
+end
+return P
+`
+	if err := ps.LoadSource("httpprobe", src); err != nil {
+		t.Fatalf("load: %v", err)
+	}
+	got, err := ps.Call("httpprobe", "probe", map[string]interface{}{"url": srv.URL})
+	if err != nil {
+		t.Fatalf("call: %v", err)
+	}
+	m, _ := got.(map[string]interface{})
+	if m == nil {
+		t.Fatalf("probe returned %T, want a table", got)
+	}
+	// A nil global surfaces as {error = "attempt to call global ... (a nil value)"} —
+	// which is a table too, so the error field is what distinguishes it.
+	if e, ok := m["error"]; ok {
+		t.Fatalf("the bridge is not reachable as %s: %v", httpGlobal, e)
+	}
+	if s, _ := m["status"].(float64); int(s) != 200 {
+		t.Fatalf("status=%v body=%v, want 200 from the loopback test server", m["status"], m["body"])
+	}
+	if body, _ := m["body"].(string); !strings.Contains(body, "monthlyCredits") {
+		t.Fatalf("body=%q, want the server's JSON", body)
+	}
+}