Add minimum-latency merged release admission

[mberman84]

Summary

• add pipeline.release_admission = "merged" and make it the default
• default batch settling to zero and drain independent bounded batches back-to-back
• keep CI, deploy, health, receipt, and superseded-release tracking asynchronous and fail-closed
• preserve exact-head authorization, configured gates, trusted coordinator boundaries, integration rules, and newest-main deployment safety
• update CLI, MCP, Action workflow, adapters, skills, examples, and reference docs for v0.2.25

Verification

• python3 -m unittest discover -s tests (285 passed)
• python3 -m ruff check .
• structured autoreview: clean, no accepted/actionable findings

This PR is intentionally draft. It has not been merged or deployed.