Add API media generation support across Pixelle workflows

[hit-cxf]

Summary

This PR adds direct API-based media generation support to Pixelle-Video, enabling image, video, and VLM capabilities without requiring ComfyUI/RunningHub for supported workflows.

What Changed

• Added API media adapters for image/video generation providers:
  • Image: DashScope Wan, Seedream, OpenAI image models
  • Video: DashScope Wan/HappyHorse, Kling, Seedance
  • VLM/LLM clients for asset analysis and prompt support
• Integrated API media generation into major WebUI workflows:
  • Quick Create / Standard
  • Image-to-Video
  • Action Transfer
  • Digital Human
  • Asset-Based custom media workflow
• Added API VLM-based asset analysis for the Asset-Based workflow, reducing dependency on ComfyUI for material evaluation.
• Added dynamic video template support in Standard mode.
• Improved video generation robustness:
  • Retry handling for transient network/download failures
  • Prompt safety retry for content-inspection failures by neutralizing prompts with LLM
  • Duration alignment with narration audio where applicable
  • Better continuity for Asset-Based video generation using previous segment tail frames
• Added history persistence support for WebUI workflows so successful generations are recorded consistently.
• Added API provider configuration examples in config.example.yaml.

Notes

• Existing self-hosted/RunningHub workflows are preserved.
• API workflows are exposed as additional provider-backed options.
• Playwright remains required for HTML rendering; browser binaries still need installation via playwright install chromium.

Verification

• Verified Standard quick-create image generation.
• Verified Standard dynamic video flow wiring.
• Verified Action Transfer API workflow.
• Verified history persistence for multiple WebUI workflows.
• Ran Python compile checks on modified modules during development.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}