Sync OpenAI and Wan docs with latest Docs repo updates

[Copilot]

This updates the openai/ and wan/ documentation packages to match the latest upstream Docs changes. The sync primarily aligns guide content and restores README endpoint coverage for newly documented OpenAI surface area.

• OpenAI README sync

  • Replaced the broken embeddings row placeholder with the correct title and local guide link
  • Added missing endpoint entries for:
    • /openai/models
    • /openai/tasks
  • Normalized OpenAI guide links to local docs/*.md files for the documented endpoints

• OpenAI guide refresh

  • Synced all OpenAI integration guides from the Docs source of truth:
    • chat completions
    • 4o image chat completions
    • embeddings
    • image edits
    • image generations
    • responses
    • tasks
  • Brought application/auth flow and request examples back in line with current upstream docs

• Wan guide refresh

  • Synced both Wan guides from the Docs source of truth:
    • videos generation
    • tasks
  • Updated application flow, request examples, and linked documentation references to match upstream

• Resulting README coverage

  | OpenAI Models API | `/openai/models` | — |
  | OpenAI Tasks API | `/openai/tasks` | [OpenAI Tasks API Integration Guide](docs/openai_tasks_api_integration_guide.md) |

[Germey]

Superseded by new sync trigger; Copilot will open a fresh PR for the latest Docs state.