Gitea reusable workflow secret exposure in pull_request_target

Gitea resolves local reusable workflow files from a fork's head commit when a trusted base-branch workflow runs for a pull_request_target event. A fork author can modify a referenced reusable workflow so attacker-controlled code executes with the repository and organization secrets available to that event. Exploitation requires a base workflow that calls a local reusable workflow, and bypasses the intended separation between trusted base code and untrusted fork code.