fastify: upgrade 4.28.0 -> 5.2.1

[mreishus]

Upgrade Fastify from v4 to v5

This PR upgrades Fastify to version 5. After reviewing our codebase against the official migration guide, no code changes were required because:

1. We're already running on Node.js v20 (Fastify v5 requirement)

2. Our codebase doesn't use any deprecated Fastify v4 features:

   • Our route handlers use consistent async/await and promise patterns
   • We don't use any deprecated request/reply properties
   • Our .listen() calls already use the new object-based signature
   • We don't use schema validation features that would require updates

3. Our current usage patterns are compatible with v5:

   • Simple logger configuration using boolean values
   • Standard request properties (request.query, request.headers)
   • Standard reply methods (reply.code(), reply.header(), reply.send())
   • GET and OPTIONS routes only (no affected DELETE routes)

Test/Verify

npm install, then npm test or npm start and testing all existing endpoints:

• / (index)
• /health-check
• /file
• /get