feat: add macOS installation script

[lmfreite]

BillionMail Pull Request Template

PR Title Format

<type>(<scope>): <description>
Examples:

• fix(smtp): handle connection timeout during bulk send
• feat(campaign-ui): add A/B testing template selector

Type Guidelines

fix      : Bug fixes (e.g., `fix(auth): prevent login loop`)  
feat     : New features (e.g., `feat(analytics): add real-time dashboard`)  
build    : Build system changes (Docker/dependencies)  
ci       : CI/CD workflows (GitHub Actions)  
docs     : Documentation updates  
style    : Code formatting (non-functional changes)  
refactor : Code restructuring (no functionality change)  
perf     : Performance improvements  
test     : Test-related changes  
chore    : Maintenance/tooling changes  

Rules:

• Scope: Specify module (e.g., smtp) or layer (e.g., frontend)
• Description:
  • Use present tense verbs (e.g., add not added)
  • No ending punctuation, max 76 chars

---

Linked Issues

Add one of these at the PR description's start:

• Fixes #1234 → Complete resolution
• Updates #1234 → Partial fix/related update

---

Branch Management

Frontend Specific

• Target Branch: dev-frontend (All frontend PRs must use this)
• Naming Convention:

# Feature development
feat/[description]  # e.g., feat/ab-test-ui
# Bug fixes
fix/[issue-id]-[desc]  # e.g., fix/4567-template-render

Backend/Core

• Target Branch: main
• Naming Convention:

# Mail engine
smtp/[feature]  # e.g., smtp/rate-limit
# Infrastructure
infra/[change]  # e.g., infra/redis-cluster

---

PR Description Template

### Purpose  
<!-- Why this change is needed (reference project goals) -->

### Implementation  
<!-- Key code/architecture changes, especially for SMTP/Rspamd -->

### Testing  
- [ ] Unit tests passed (`npm test`/`go test`)  
- [ ] Manual steps:  
~~~bash
# Example: Test bulk send
bm send --campaign test --list 1000
~~~
- [ ] Impact analysis (e.g., template compatibility/sending rate)

### Additional Context
<!-- Screenshots, performance metrics, or related docs -->

---

Automation Integration

1. Commit Validation:
   Use husky + commitlint to enforce conventions:

// commitlint.config.js
module.exports = { extends: ['@commitlint/config-conventional'] };

2. PR Title Check:
   Add GitHub Action to validate PR titles:

# .github/workflows/pr-check.yml
uses: amannn/action-semantic-pull-request@v5

Tip: For mail-sending logic changes, verify SPF/DKIM signing

### Key Features
- **Frontend Isolation**: Explicit `dev-frontend` branch for frontend changes  
- **Modular Scopes**: Clear module boundaries (e.g., `smtp`, `analytics`) for automated changelogs  
- **Compliance Ready**: GDPR/SPF checks emphasized for critical components  

This template can be saved to `.github/PULL_REQUEST_TEMPLATE.md` for automatic application.