Enable two overlapping Platform merge-group builds #892

🤖 Generated by the Agentic Engineer

Platform's active merge queue dispatches one build at a time. To start validating the next PR while the first deploys, raise the repository-managed build limit to two. Keep one PR per merge, require all checks, and preserve the existing timeout and ruleset scope.

The production ordering guard in devantler-tech/platform#6036 must merge and pass its native deploy before this change is applied. Read back the GitHub ruleset after reconciliation and use real merge-group runs to verify overlap and measure total queue time. Measurement is tracked in devantler-tech/platform#6035.