Add request size limits to prevent memory exhaustion attacks

[greatm3]

Currently, the server has no limit on incoming request size. An attacker can send infinite data and crash the server through memory exhaustion.

Tasks:

• Add MAX_REQUEST_SIZE constant (recommend 1MB = 1024 * 1024 bytes)
• Track totalBytes in the data event handler
• Check if totalBytes > MAX_REQUEST_SIZE before processing
• Respond with HTTP/1.1 413 Payload Too Large when limit exceeded
• Close connection after sending 413 response

Files to modify:

• src/httpServer.ts - data event handler

References:

• RFC 7230 Section 3.3.2 (Message Body Length)
• OWASP: Denial of Service via resource exhaustion