Tempus DDB v0.4.0

First public beta of the fail-closed B2A security gate for autonomous agent actions. Includes signed policy bundles, workload identity lifecycle, credential-isolated GitHub execution, and verifiable execution receipts.\n\nThis beta is validated across Python 3.10 and 3.12 on Linux, macOS, and Windows. It is intended for single-instance deployments; independent external checkpoints and multi-instance durability remain future work.