Add AI video generator FastAPI app with web UI and image->MP4 pipeline

[reoreoxzkami]

Motivation

• Provide a simple web application that generates short MP4 videos from text prompts by composing AI-generated or fallback images.
• Include a lightweight browser UI for prompt entry, preview, and download of generated videos.
• Support using OpenAI gpt-image-1 when OPENAI_API_KEY is available with a graceful fallback when not.

Description

• Add main.py which implements a FastAPI app with endpoints GET / (UI), POST /generate, GET /download/{file_name}, and GET /video/{file_name} and mounts /static and Jinja templates.
• Implement image generation via _openai_images that calls OpenAI images API (gpt-image-1) or _fallback_image that creates a gradient + prompt overlay when no API key is present.
• Build video files by concatenating frames with MoviePy in _build_video and save outputs to the generated/ directory.
• Add templates/index.html browser UI for prompt/scene configuration and client-side handling to call POST /generate and preview/download results.
• Add requirements.txt for dependencies and README.md with setup and usage instructions and uvicorn startup example.

Testing

• No automated tests were added or executed for this change.

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[chatgpt-codex-connector]

Ensure static directory exists before mounting

StaticFiles(directory="static") validates the directory at startup, but this commit does not add a static/ folder, so a fresh checkout following the README will fail to boot with a runtime error before any endpoint is served. This makes the app unusable out of the box unless users manually create an empty directory.

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