Perturb

First maintainer-reviewed pass for SN26 (previously unreviewed, categories empty, no website/source-repo surfaces despite website_url/source_repo already being set). Perturb is an adversarial-robustness network: miners find imperceptible perturbations that fool image classifiers (fixed EfficientNetV2-L on ImageNet-100), validators verify and score. Added the missing website and source-repo surfaces. Checked the website for additional surfaces beyond what was already tracked: /playground is a hands-on interactive demo (image upload), not a data feed or leaderboard -- not tracked. No OpenAPI schema or separate docs subdomain found.