Arbitrary file write via prompt path traversal

Path traversal in DirectoryPromptRegistry.set() in Banks before 2.4.5 allows remote authenticated users to write files via crafted prompt fields. The method builds a filesystem path from untrusted Prompt.name and Prompt.version values, accepts dot segments and absolute names, writes Prompt.raw to the resolved path, and _load() later reconstructs the poisoned path from index.json. Exposure requires an application to pass user-controlled prompt metadata into the registry; overwrite=True also replaces existing writable files, but the documented impact is bounded to paths writable by the application process.