feat: add MuAPI video generation tool

[Anil-matcha]

Summary

Adds tools/video/muapi_video.py — a video generation tool backed by muapi.ai, a unified API aggregator for 400+ generative media models.

What this adds

• MuApiVideo tool following the BaseTool contract (same pattern as seedance_video.py, kling_video.py)
• Text-to-video: Veo3, Veo3-fast, Kling, Wan 2.1/2.2, Seedance Pro, Runway, Pixverse, HunyuanVideo, Minimax
• Image-to-video: Kling, Wan, Seedance, Runway, Pixverse, Vidu, HunyuanVideo
• Async submit → poll pattern matching muapi's API contract
• get_status() checks for MUAPI_API_KEY env var
• estimate_cost() based on per-second pricing

Setup

export MUAPI_API_KEY=your_key_here
# Get one at https://muapi.ai/dashboard/api-keys

Example

from tools.video.muapi_video import MuApiVideo

tool = MuApiVideo()
result = tool.execute({
    "prompt": "A cinematic drone shot over a misty mountain lake at sunrise",
    "operation": "text_to_video",
    "model_variant": "veo3-fast",
    "duration": 5,
    "aspect_ratio": "16:9",
    "output_path": "output.mp4",
})
print(result.data["output"])