feat(plugins): 方舟 Agent Plan - 新增图片与视频协议插件

独立 /api/plan/v3 Seedream、Seedance 插件，并同步宿主能力默认值与渠道识别，避免与官方 /api/v3 凭证混用。

Co-authored-by: Cursor <cursoragent@cursor.com>

web/test/model-protocols.test.ts

@@ -6,8 +6,10 @@ describe("model protocol Token billing", () => {
     test("supports text models and Volcengine Ark video only", () => {
         expect(modelProtocolSupportsTokenBilling("text", "chat-completion")).toBe(true);
         expect(modelProtocolSupportsTokenBilling("video", "volcengine-ark-video")).toBe(true);
+        expect(modelProtocolSupportsTokenBilling("video", "volcengine-ark-agent-plan-video")).toBe(true);
         expect(modelProtocolSupportsTokenBilling("video", "volcengine-jimeng-video")).toBe(false);
         expect(modelProtocolSupportsTokenBilling("video", "newapi")).toBe(false);
         expect(modelProtocolSupportsTokenBilling("image", "volcengine-ark-image")).toBe(false);
+        expect(modelProtocolSupportsTokenBilling("image", "volcengine-ark-agent-plan-image")).toBe(false);
     });
 });