Introduce `relax_csp_for_remote_media` middleware that modifies Content Security Policy headers to permit loading media from trusted external domains (Civitai and Genur). This is necessary for LoRA Manager UI previews when ComfyUI runs with `--disable-api-nodes`, which otherwise blocks remote images and videos. The middleware is inserted after ComfyUI's `block_external_middleware` to properly extend the restrictive CSP header.
