Heartbeat client now reads master connection settings from the agent
config ([master] section) with env var fallback. Includes address,
ca_cert, token_path, and role fields.
Agent's Run() creates and starts the heartbeat client automatically
when [master] is configured.
Tested on all three nodes: rift (master), svc (edge), orion (worker)
all registered with the master and sending heartbeats every 30s.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>