feat(blueprints): add GitOps PostgreSQL zero-downtime migration verifier and lock risk guard - #343

What

Adds an enterprise-grade production workflow blueprint: GitOps PostgreSQL Zero-Downtime Migration Verifier and Lock Risk Guard (flows/gitops-postgres-migration-guard.yaml).

Blueprint

• File: flows/gitops-postgres-migration-guard.yaml
• ID: gitops-postgres-migration-guard
• Namespace: company.team
• Tags: Infrastructure, Data, Cloud

What it does

1. GitOps Webhook & Event Integration: Triggered automatically by GitHub Actions CI when pull requests introduce or modify SQL migration files.
2. DDL AST Static Lock Analysis: Runs comprehensive static analysis over migration DDL inspecting:
   • ACCESS EXCLUSIVE lock escalation (column type changes, unconstrained ALTER TABLE, adding non-null columns without defaults).
   • Missing CONCURRENTLY keyword on CREATE INDEX and DROP INDEX.
   • Foreign key constraints created without supporting indexes (causing table-level share locks on parent tables).
   • Circular Row-Level Security (RLS) recursion anti-patterns without SECURITY DEFINER wrappers.
3. Transactional Dry-Run Sandbox: Executes the migration against a staging PostgreSQL database inside an explicit BEGIN ... ROLLBACK transaction block using io.kestra.plugin.jdbc.postgresql.Queries to measure execution time and verify SQL syntax with zero persistent side effects.
4. Risk Evaluation Gate & GitHub/Slack Feedback:
   • High-Risk: Dispatches emergency Slack alert with anti-pattern analysis and recommended safe SQL rewrites.
   • Safe: Issues certification approval and logs deployment clearance.
5. Audit Logging & Resilient Error Handling: Emits structured compliance records with full lineage.

Prerequisites

• Staging PostgreSQL instance URL (STAGING_POSTGRES_URL).
• Slack Incoming Webhook URL (SLACK_WEBHOOK_URL).
• Migration Webhook Secret Key (MIGRATION_WEBHOOK_KEY).

Validation

• PyYAML syntax validated.
• Blueprint tag workflow (.github/workflows/validate-blueprint-tags.yml) verified: valid tags, metaDescription length <= 160 characters.
• 100% emoji-free output.