When block streaming succeeds, final replies are dropped but TTS was only
applied to final replies. Fix by accumulating block text during streaming
and generating TTS-only audio after streaming completes.
Also:
- Change truncate vs skip behavior when summary OFF (now truncates)
- Align TTS limits with Telegram max (4096 chars)
- Improve /tts command help messages with examples
- Add newline separator between accumulated blocks
