Make Newman integration checkpoints authoritative

[jmjava]

Summary

• stop passing --skip-integration in normal operator-backed cluster CI
• clean stale Newman resources before execution so assertions cover only the current run
• require the bootstrap StackRun to reconcile to a PipelineRun
• fail on fetch-source failure, PipelineRun failure, or checkpoint timeout
• retain explicit skip behavior only when operator installation is explicitly disabled
• gate script and Postman contract changes in cluster CI and pin Newman 6.2.1
• record M17.10 acceptance evidence

Verification

• all 15 checks passed on implementation commit 2e5ea04
• cluster-regression run 34989095946: passed authoritative StackRun/PipelineRun/fetch-source checkpoint
• bash scripts/run-regression-agent.sh: regression exit code: 0 (local-only)
• M17.10 static acceptance tests: pass
• Bash syntax, ShellCheck, Ruff, and strict workflow YAML parsing: pass