fix(e2e): 修复ESM模式下__dirname未定义导致Staging E2E失败

根因：Playwright在ESM模式下运行，CommonJS的__dirname全局变量不存在。
修复：使用fileURLToPath(import.meta.url) + path.dirname 实现ESM兼容的__dirname。

影响用例：
- core-generation.spec.ts: walks through 5-step wizard and starts generation
- core-upload.spec.ts: uploads a video asset and shows it in the asset library

apps/web/e2e/core-generation.spec.ts

@@ -1,7 +1,9 @@
 import { expect, test, type APIRequestContext } from "@playwright/test"
 import * as fs from "node:fs"
 import * as path from "node:path"
+import { fileURLToPath } from "node:url"
 
+const __dirname = path.dirname(fileURLToPath(import.meta.url))
 const PASSWORD = "SmokePass123!"
 const apiBase = process.env.E2E_API_BASE || "/api/v1"
 const apiOrigin = apiBase.endsWith("/api/v1") ? apiBase.slice(0, -"/api/v1".length) : ""

apps/web/e2e/core-upload.spec.ts

@@ -1,7 +1,9 @@
 import { expect, test, type APIRequestContext } from "@playwright/test"
 import * as fs from "node:fs"
 import * as path from "node:path"
+import { fileURLToPath } from "node:url"
 
+const __dirname = path.dirname(fileURLToPath(import.meta.url))
 const PASSWORD = "SmokePass123!"
 const apiBase = process.env.E2E_API_BASE || "/api/v1"
 const apiOrigin = apiBase.endsWith("/api/v1") ? apiBase.slice(0, -"/api/v1".length) : ""