Align with healthy gemini-eraser-ai space: remove CLIPSeg/transformers, use RealESRGAN_x4plus.pth from GitHub

Fix: download RealESRGAN x4 from GitHub instead of COPY missing 4x-UltraSharp.pth

Fix model loading: use absolute paths, retry logic, proper model assignment

Update backend with text segmentation, UltraSharp, and lossless compositing

Upgrade backend to use Real-ESRGAN

feat: FSRCNN AI upscaling endpoint via OpenCV dnn_superres (PRO feature)

Bake FastSAM weights into Docker image to avoid RO filesystem error

chore: update project metadata, dependencies, and Docker configuration

Initial commit for HF Spaces backend