feat: customise tts /tmp dir using environment variable

/tmp is normally part of OS disk , for high volume calls its important to have tts file on high storage space , hence its needed have environment variable

No file, entry point, environment-variable name, or test is identified. Locate the TTS temporary-file handling and inspect existing configuration patterns first; the work is done when a documented environment variable controls the TTS temp directory and tests cover the configured location without changing the default.

Written by the indexing model from the issue text.