Add agent forwarding of boundary audit logs from workspaces to coderd
via agent API, and re-emission of boundary logs to coderd stderr. This
change adds a server to the workspace agent that always listens on a
unix socket for boundary to connect and send audit logs.
coderd log format example:
```
[API] 2025-12-23 18:31:46.755 [info] coderd.agentrpc: boundary_request owner=.. workspace_name=.. agent_name=.. decision=.. workspace_id=.. http_method=.. http_url=.. event_time=.. request_id=..
```
Corresponding boundary PR: https://github.com/coder/boundary/pull/124
RFC:
https://www.notion.so/coderhq/Agent-Boundary-Logs-2afd579be59280f29629fc9823ac41bahttps://github.com/coder/coder/issues/21280
Zach