Agent Fabric (Synadia Agent Protocol) is the headline of this release:
defineNatsAgent / useAgents / getAgentStatuses, agent-aware health
endpoint, and an extended error-isolated shutdown sequence.

- CHANGELOG: add 0.1.0-alpha.3 section; correct alpha.2 date (was
  mislabelled 'unreleased' — shipped 2026-05-29)
- README: Agent Fabric feature bullet + host/call usage examples
- docs/index.md: link the Agent Fabric guide
- docs/api.md: document defineNatsAgent, useAgents, getAgentStatuses,
  stopAllAgents, and the agents[] health field
- package.json: 0.1.0-alpha.2 -> 0.1.0-alpha.3