Add asynchronous job control also for small texts.

[hastla007]

It would be usefull for automations (like n8n) to enhance the API for asynchronous job control also for small texts — same job management model (create, check status, download result).

Currently the main API only supports:

/audio/speech → sync (immediate response)
/audio/speech/long → async (background jobs, but requires >3000 chars)

It would be great to have for example:

/audio/speech/async

→ behaves like /audio/speech/long, but also accepts texts under 3000 chars, and handles them in background queue.

[hastla007]

I removed hardcoded limit and made it configurable in env and docker compose files.

#52