Fix Windows claim startup and restore JSON demo

[jakthom]

Summary

• start the initial claim deadline only after the claim goroutine is scheduled, preventing scheduler delay from being reported as an unreachable gateway
• preserve the bounded timeout for a genuinely blocked initial bus write
• restore the README terminal demo to JSON wire values and expand it to 18 representative PGNs
• clarify that the demo projects the metadata envelope down to the PGN for readability

Verification

• go test ./...
• just pgn-sync-check
• just lint
• just secure
• just test-race
• Windows amd64 test-binary cross-compile
• 100 consecutive runs of TestBroadcast_PeriodicTransmission
• SVG XML validation and full-state render review