KeyringSeam: macOS Keychain Credential Provider for DeepSeek Harness

`fieldnote-ops/keyringseam` is a macOS Keychain credential provider plugin for DeepSeek Harness (DSH), designed to address the weak permission boundaries of managed credentials within the `ctx.credentials` seam. This project is independently maintained, supports macOS 13+, is licensed under the MIT license, and the current public version is v0.2.0-rc.1. Its core mechanism involves using an Apple-notarized Developer ID-signed Broker application to store sensitive values in a private Data Protection Keychain access group, and explicitly requiring device owner authentication before each credential retrieval, setting, or cancellation. The plugin provides