Added guardrail and agent templates

[MikeTheCyberGuy]

Introduce AI4SDLC template baseline: agents, guardrails, and platform overlays

Overview

This PR adds a standardized AI4SDLC template baseline to support governed AI usage in software delivery. The intent is to make AI-assisted changes reviewable, repeatable, and policy-aligned out of the box.

Key additions

• Policy + governance scaffolding (templates/.ai4sdlc/POLICY/*): guardrails (md/yaml), autonomy levels, and tool allowlist
• Agent definitions (templates/.ai4sdlc/AGENTS/*): validator role plus supporting personas (security analyst, test planner, requirements, red team prompting, control mapping, etc.)
• Prompt + review artifacts (templates/.ai4sdlc/PROMPTS/*, templates/.ai4sdlc/FORMS/*, review templates): standardized intake/checklists and reusable prompts
• Platform overlays (templates/platform_overlays/gitlab/*, templates/.gitlab/*): GitLab Duo rules, MR templates, and CI safety include scaffolding for GitLab-based workflows
• Supporting documentation (templates/* and templates/docs/*): quickstart + governance docs to help teams adopt the templates consistently

Impact

• Additive-only templates/docs; no production application logic changes.
• Provides a drop-in, auditable baseline for AI-assisted SDLC with clear safety boundaries and traceable review structure.