feat(pdf): add timeout guard for PDF generation (#762)

[CyberXpert607]

Summary

Implements #762: Adds timeout guard for PDF generation to prevent hanging connections.

Changes Made

1. Timeout Utility (src/lib/timeout.ts)

• ✅ Reusable withTimeout function using Promise.race
• ✅ Proper timer cleanup to prevent memory leaks

2. PDF Generation Service (src/services/pdf-generation.ts)

• ✅ Full Puppeteer-based PDF generation
• ✅ page.setDefaultTimeout(25000)
• ✅ Browser cleanup in finally block
• ✅ Removed any type with proper Certificate interface

3. Certificate Download Route (src/app/api/certificates/[id]/download/route.ts)

• ✅ Wrapped PDF generation with 30s timeout
• ✅ HTTP 504 on timeout with retry message
• ✅ Proper unknown error handling

4. Generic PDF Generation Route (src/app/api/generate-pdf/route.ts)

• ✅ Same timeout handling and 504 response
• ✅ Proper unknown error handling

5. Integration Test

• ✅ Mocks slow PDF generation
• ✅ Asserts 504 response with error payload

6. Environment Variable

• ✅ PDF_TIMEOUT_MS=30000 added

Scope Note

Only files directly related to #762 were modified. No other files were touched.

Related Issue

Closes #762

Checklist

• PDF generation bounded by 30-second timeout
• HTTP 504 returned on timeout with retry message
• Puppeteer timeout set to 25 seconds
• Integration test added
• Browser cleanup on timeout
• Timeout configurable via environment variable
• No out-of-scope files modified

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[RUKAYAT-CODER]

Great job so far

There’s just one blocker — workflow failing. Could you take a look and resolve it?

Happy to review again once that’s done.