feat: add tailored AGENTS.md instruction file for AI coding tools

## Summary

Modern AI coding tools (Claude Code, Cursor, Copilot, Antigravity, Aider) automatically read root instruction files (`AGENTS.md` / `CLAUDE.md`) on repository startup without requiring any manual developer configuration or setup scripts.

Adding a tailored `AGENTS.md` to `bcgov/quickstart-openshift` will ensure that any AI agent working on a repository instantiated from this template immediately inherits the technical rules, architecture conventions, and quality gates of the stack out of the box.

## Proposed `AGENTS.md` Content & Specification

The `AGENTS.md` file should provide explicit, non-ambiguous guidance tailored to the `quickstart-openshift` stack:

### 1. Stack & Directory Architecture
* **Backend**: NestJS (TypeScript) in `backend/`.
* **Frontend**: TypeScript / Caddy in `frontend/`.
* **Database & Migrations**: PostgreSQL/PostGIS. All schema changes **must** be authored as Flyway SQL scripts under `migrations/sql/`.
* **Infrastructure**: OpenShift manifests and GitHub Actions workflows under `.github/`.

### 2. Code Quality & Guardrails
* **TypeScript Strictness**: Enforce strict typing. No implicit `any` or `@ts-ignore` suppressions.
* **Secret Safety**: Strictly forbid committing `.env`, `application.properties`, or hardcoded credentials.
* **Commit Conventions**: Enforce Conventional Commits (`feat:`, `fix:`, `chore:`).
* **Dependency Safety**: Bypassing peer dependencies (`--legacy-peer-deps`) is strictly prohibited.

### 3. Verification & Execution Commands
* **Local Stack**: `docker compose up -d`
* **Migrations**: Handled via `migrations` Flyway container.
* **Testing**: Run containerized tests (`docker compose exec backend npm test`).

## Value
* **Zero developer setup**: Agents automatically load the file on repository open.
* **Prevents AI hallucinations**: Guides agents to use Flyway SQL migrations instead of inline ORM sync, enforces TypeScript strictness, and prevents secret leaks.