feat: Add cloud E2E testing infrastructure

Adds Playwright tests for cloud environment with Firebase auth.

Changes:
- Refactor ComfyPage to abstract base class
- Add LocalhostComfyPage (existing devtools implementation)
- Add CloudComfyPage (cloud settings API, Firebase auth)
- Add cloud fixture with auth state persistence
- Add globalSetupCloud for Firebase login
- Add playwright.cloud.config with 5x timeout
- Add basic cloud tests (load app, canvas interaction, settings)
- Update .gitignore for auth state files
- Update tsconfig to include playwright.cloud.config

Architecture:
- ComfyPage abstract with 3 backend-specific methods
- LocalhostComfyPage uses /api/devtools + multi-user
- CloudComfyPage uses /api/settings + Firebase localStorage
- No code duplication (95% shared)

Setup:
- Requires CLOUD_TEST_EMAIL and CLOUD_TEST_PASSWORD env vars
- globalSetup logs in once, saves auth to browser_tests/.auth/
- Tests reuse saved auth state (no login per test)

browser_tests/fixtures/LocalhostComfyPage.ts

@@ -0,0 +1,74 @@
+import type { APIRequestContext, Page } from '@playwright/test'
+
+import { ComfyPage } from './ComfyPage'
+import type { FolderStructure } from './ComfyPage'
+
+/**
+ * Localhost-specific implementation of ComfyPage.
+ * Uses devtools API and multi-user mode for test isolation.
+ */
+export class LocalhostComfyPage extends ComfyPage {
+  constructor(page: Page, request: APIRequestContext) {
+    super(page, request)
+  }
+
+  async setupWorkflowsDirectory(structure: FolderStructure): Promise<void> {
+    const resp = await this.request.post(
+      `${this.url}/api/devtools/setup_folder_structure`,
+      {
+        data: {
+          tree_structure: this.convertLeafToContent(structure),
+          base_path: `user/${this.id}/workflows`
+        }
+      }
+    )
+
+    if (resp.status() !== 200) {
+      throw new Error(
+        `Failed to setup workflows directory: ${await resp.text()}`
+      )
+    }
+
+    await this.page.evaluate(async () => {
+      await window['app'].extensionManager.workflow.syncWorkflows()
+    })
+  }
+
+  async setupUser(username: string): Promise<string | null> {
+    const res = await this.request.get(`${this.url}/api/users`)
+    if (res.status() !== 200)
+      throw new Error(`Failed to retrieve users: ${await res.text()}`)
+
+    const apiRes = await res.json()
+    const user = Object.entries(apiRes?.users ?? {}).find(
+      ([, name]) => name === username
+    )
+    const id = user?.[0]
+
+    return id ? id : await this.createUser(username)
+  }
+
+  private async createUser(username: string): Promise<string> {
+    const resp = await this.request.post(`${this.url}/api/users`, {
+      data: { username }
+    })
+
+    if (resp.status() !== 200)
+      throw new Error(`Failed to create user: ${await resp.text()}`)
+
+    return await resp.json()
+  }
+
+  async setupSettings(settings: Record<string, any>): Promise<void> {
+    const resp = await this.request.post(
+      `${this.url}/api/devtools/set_settings`,
+      {
+        data: settings
+      }
+    )
+
+    if (resp.status() !== 200) {
+      throw new Error(`Failed to setup settings: ${await resp.text()}`)
+    }
+  }
+}