USB: A trust layer for AI skills and MCP servers

USB is an open-source trust layer for AI capabilities that discovers skills, MCP servers, agents and commands in repositories, compares declared behavior against observable evidence with secscan, and observes live MCP servers with mcprobe. It ships a 529-skill catalog and a 16-target installer (four native runtime installs plus portable bundles), with secscan producing deterministic verdicts and file:line evidence and exit codes for CI, while mcprobe requires explicit consent and never calls a tool. The project is at v1.0.8 under the MIT license.