Extend scroll idle timeout to 30 minutes

[MarcStdt]

Summary

• change all scroll keepAliveTraffic windows from 5m to 30m while preserving traffic thresholds
• update generated scroll YAML plus build templates/vars so make build-tree keeps the new window
• update README guidance for Minecraft keepAliveTraffic

Validation

• make build-tree
• go test ./scripts/prebuild
• go test ./scripts/validate-release-workflow
• go run ./scripts/validate-scrolls.go
• ./scripts/validate_all_scrolls.sh
• git diff --check

[druid-infra]

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