Add new endpoint that returns server start time and uptime duration in seconds.
The endpoint follows the same pattern as handleHealth and handleInfo handlers,
using the existing startedAt field from the Server struct.
Response format:
{
"start_time": "2026-05-05T19:30:00Z",
"uptime_seconds": 1234
}
Includes unit tests with httptest.NewRecorder() to verify JSON response
structure and content type headers.
Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>
