This PR introduces robust server lifecycle management, atomic server state tracking, and improved health endpoint reporting to the whisper.cpp HTTP server.

Key Changes

• Graceful Shutdown:
  • Implements cross-platform signal handling (SIGINT/SIGTERM, Ctrl+C) for clean server shutdown.
  • Double Ctrl+C forces immediate termination for developer convenience.
• Atomic Server State:
  • Adds an atomic server_state variable to track model loading and readiness.
  • Ensures thread-safe state transitions during model (re)loading.
• Health Endpoint Enhancement:
  • /health endpoint now returns 503 and a loading message if the model is not ready.
  • Returns 200 and {"status":"ok"} when the server is ready.
• Threaded Server Execution:
  • Runs the server in a dedicated thread to allow responsive signal handling and proper resource cleanup.
• Smart Pointer Usage:
  • Refactors server object management to use std::unique_ptr for safer resource handling.
• General Refactoring:
  • Updates all server method calls for smart pointer usage.
  • Adds a cleanup routine to free resources on shutdown.

Motivation

• Improve production robustness and observability.
• Enable safe and predictable shutdowns for deployment and development.
• Provide accurate health status for orchestration and monitoring systems.

Testing

• Manual testing on macOS and Linux for signal handling and health endpoint responses.
• Verified model loading, reloading, and shutdown behavior.
• Confirmed /health endpoint returns correct status during all server states.