agent-credential-broker: fork of vaultwarden-agent-broker + OpenBao backend

Mechanical rename (package agent_credential_broker; entry points
agent-broker{,-mcp,-plugin}; env AGENT_BROKER_*; paths agent-broker;
agent-browser credential provider 'broker'; MCP server name agent-broker).

New backend 'openbao': stdlib-only HTTP client for OpenBao/Vault KV v2
(approle login or token file/env; metadata-only ref index; lazy re-login
on 401/403; token renewal). bitwarden-cli backend kept as transition.

pyproject.toml

@@ -0,0 +1,18 @@
+[build-system]
+requires = ["setuptools>=61"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "agent-credential-broker"
+version = "0.1.0"
+description = "Capability layer: agents use vault credentials (OpenBao / Bitwarden-compatible) without ever reading them"
+requires-python = ">=3.10"
+dependencies = []
+
+[project.scripts]
+agent-broker = "agent_credential_broker.cli:main"
+agent-broker-plugin = "agent_credential_broker.plugin:main"
+agent-broker-mcp = "agent_credential_broker.mcp_server:main"
+
+[tool.setuptools.packages.find]
+include = ["agent_credential_broker*"]