* ci: move Postgres, MCP and Redis suites to CircleCI integration
* ci: throwaway, drop tests/proxy_behavior from its CircleCI job to show assert-ci-coverage fails
* ci: revert throwaway assert-ci-coverage check
* ci: keep the e2e helpers the gate tests still use
* ci: move the roi-database Postgres shard to CircleCI integration
* ci: run redis-compat without CircleCI's Azure and cassette env, cover postgres_suite test_path
* ci: match the GitHub env for the moved Postgres and Redis jobs
* ci: unset provider keys in the CircleCI MCP job and drop unused e2e-stack helpers
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Co-authored-by: yuneng <yuneng@berri.ai>