test: add API seeding infrastructure and app creation E2E scenarios

[Jingyi-Dify]

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Summary

• Introduces e2e/support/api.ts with createTestApp / deleteTestApp
  helpers that call the console API directly using the stored Playwright
  session, enabling fast and isolated test-data setup without UI flows
  • Extends DifyWorld with per-scenario state for app name tracking,
    seeded app ID cleanup, and download capture
  • Wires automatic cleanup into the After hook so every seeded app is
    deleted after each scenario, regardless of pass/fail
  • Adds E2E scenarios for the three previously uncovered app creation
    modes: Agent, Chatflow (Advanced Chat), and Text Generator (Completion)

Test plan

• pnpm -C e2e check passes (type-check + lint)
• CI E2E run covers @apps @core tag scenarios
• Seeded apps are removed from the workspace after each test run

Screenshots

Before	After
...	...

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods