Legacy POC owner for one standalone timeless-traces-api executable.

This reuses the lifecycle proven by the metrics POC: the Rust child alone owns its database, readiness follows its listener announcement, abnormal exit is isolated for supervisor restart, and normal OTP termination sends SIGTERM and waits for drain/reaping. Production releases must use the Phoenix control-plane owner instead. This module is retained only for POC compatibility tests and is never selected implicitly by HistoricalSource.