The `frames_after_eos` parameter in `generate_audio_stream()` and
`generate_audio()` was accepted but never used - the code always used
the auto-calculated guess.
**Before:** User passes `frames_after_eos=0` → ignored, uses guess (3+
frames of silence)
**After:** User passes `frames_after_eos=0` → respected, minimal
trailing silence
Default behavior preserved when `frames_after_eos=None`.
I *think* this is the intention of that argument.
