feat: add observability schema foundations

[peg]

Summary

• add rampart.audit.v1 audit event schema version defaults
• add local non-sensitive host context to newly written audit events
• add rampart.status.v1 output via rampart status --json
• document the new status JSON flag

Testing

• go test ./internal/audit ./cmd/rampart/cli -count=1
• go test ./... -count=1
• go vet ./...
• make build
• ./rampart status --json | python3 -m json.tool