feat(providers): add Alibaba Token Plan (token-plan.ap-southeast-1)

Fourth Alibaba key type — Coding Plan (alicode/alicode-intl) and Model Studio
(alims-intl) both reject Token Plan keys. Registry entry only; PROVIDER_MODELS
builds from providers/registry so no executor or translator work is needed.

Singapore-only (eu-central-1 answers IllegalEndpoint) and OpenAI-compatible
transport only (the Anthropic surface is not authorized for this plan).

Closes #2754
Closes #2806

tests/unit/alibaba-token-plan-provider.test.js

@@ -0,0 +1,45 @@
+import { describe, expect, it } from "vitest";
+
+import REGISTRY from "../../open-sse/providers/registry/index.js";
+import { PROVIDERS, PROVIDER_MODELS } from "../../open-sse/providers/index.js";
+
+describe("Alibaba Token Plan provider", () => {
+  const entry = REGISTRY.find((e) => e.id === "alitp-intl");
+
+  it("is registered as an OpenAI-compatible apikey provider", () => {
+    expect(entry).toBeDefined();
+    expect(entry.category).toBe("apikey");
+    expect(PROVIDERS["alitp-intl"]).toBeDefined();
+    expect(PROVIDERS["alitp-intl"].format).toBe("openai");
+  });
+
+  it("targets the Singapore Token Plan host in compatible mode", () => {
+    // eu-central-1 answers IllegalEndpoint; the plan is Singapore-only.
+    expect(PROVIDERS["alitp-intl"].baseUrl).toBe(
+      "https://token-plan.ap-southeast-1.maas.aliyuncs.com/compatible-mode/v1/chat/completions",
+    );
+  });
+
+  it("does not collide with the other three Alibaba key types", () => {
+    const hosts = ["alicode", "alicode-intl", "alims-intl", "alitp-intl"]
+      .map((id) => new URL(PROVIDERS[id].baseUrl).host);
+    expect(new Set(hosts).size).toBe(hosts.length);
+  });
+
+  it("exposes the models the plan actually serves", () => {
+    const ids = (PROVIDER_MODELS["alitp-intl"] || []).map((m) => m.id);
+    expect(ids).toEqual(expect.arrayContaining([
+      "qwen3.8-max-preview",
+      "qwen3.7-max",
+      "qwen3.7-plus",
+      "qwen3.6-flash",
+      "glm-5.2",
+      "deepseek-v4-pro",
+    ]));
+  });
+
+  it("keeps every registry id unique after adding the provider", () => {
+    const ids = REGISTRY.map((e) => e.id);
+    expect(new Set(ids).size).toBe(ids.length);
+  });
+});