[P1-11] Expand release CI gates across modules, integrations, and security

[erikhoward]

Goal

Make a release candidate prove the same build, test, and security contract as continuous integration.

Scope

• Run root, irisadapter, and examples tests/builds in the release workflow.
• Add race, integration/conformance, MCP interoperability, SQLite/PostgreSQL, gosec, and govulncheck gates.
• Define provider-credential and external-service behavior for tests without leaking secrets.
• Add a release-candidate checklist and failure diagnostics.

Acceptance criteria

• The release workflow exercises all three Go modules.
• Security and integration failures block a release candidate.
• Integration tests are reproducible locally or clearly report required services/credentials.
• No secret values appear in logs or artifacts.

Priority

P1 — release-quality engineering gap.

See the PetalFlow 1.0.0 Readiness Report for the audit context.