Add GitHub Copilot repository instructions

[Copilot]

Implements .github/copilot-instructions.md to provide Copilot with repository-specific context for code generation and reviews.

Instructions Coverage

• Architecture: Routes (HTTP handlers) → Services (business logic + external API calls)
• Security: API key management via env vars, input validation patterns, rate limiting (60 req/min)
• Code Style: CommonJS, async/await, Prettier (single quotes, 100 char width), ESLint config
• Testing: Jest patterns with descriptive names, mock external APIs
• Error Handling: Try-catch with console.error logging, HTTP status codes (400/502/500)
• Dependencies: Prefer axios for HTTP, express-rate-limit, helmet for security headers

Example Pattern

// routes/example.js
router.post('/', async (req, res) => {
  try {
    const input = req.body?.field;
    if (!input) return res.status(400).json({ error: 'Invalid input' });
    
    const result = await serviceFunction(input);
    res.json(result);
  } catch (err) {
    console.error('Operation failed:', err);
    res.status(502).json({ error: 'Operation failed' });
  }
});

File size: 437 lines (within GitHub's recommended <1000 line limit for optimal Copilot processing).

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• gh.io
  • Triggering command: curl -sL REDACTED (dns block)
  • Triggering command: curl -L -v REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>✨ Copilot instructions</issue_title>
<issue_description>Configure instructions for this repository as documented in Best practices for Copilot coding agent in your repository.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes ✨ Copilot instructions #28

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[Copilot]

Pull Request Overview

This PR adds comprehensive GitHub Copilot repository instructions to guide AI-assisted code generation and reviews. The instructions document the existing project architecture, coding standards, security practices, and development workflows for the PharmaIntel API.

• Establishes coding standards (CommonJS, async/await, Prettier/ESLint configs)
• Documents security best practices (API key management, input validation, rate limiting)
• Provides clear patterns for routes, services, testing, and error handling