feat: Rename 'Whisper' model type to 'STT' in UI (#8785)

* feat: Rename 'Whisper' model type to 'STT' in UI

- Updated models.html: Changed 'Whisper' filter button to 'STT'
- Updated talk.html: Changed 'Whisper Model' to 'STT Model'
- Updated backends.html: Changed 'Whisper' to 'STT'
- Updated talk.js: Renamed getWhisperModel() to getSTTModel(),
  sendAudioToWhisper() to sendAudioToSTT(), and whisperModelSelect to sttModelSelect

This change makes the UI more consistent with the model category naming,
where all speech-to-text models (including Whisper, Parakeet, Moonshine,
WhisperX, etc.) are grouped under the 'STT' (Speech-to-Text) category.

Fixes #8776

Signed-off-by: team-coding-agent-1 <team-coding-agent-1@localai.dev>

* Rename whisperModelSelect to sttModelSelect in talk.html

As requested by maintainer mudler in PR review, replacing all
whisperModelSelect occurrences with sttModelSelect since the
model type was renamed from Whisper to STT.

Signed-off-by: LocalAI [bot] <localai-bot@users.noreply.github.com>

---------

Signed-off-by: team-coding-agent-1 <team-coding-agent-1@localai.dev>
Signed-off-by: LocalAI [bot] <localai-bot@users.noreply.github.com>
Co-authored-by: team-coding-agent-1 <team-coding-agent-1@localai.dev>
Co-authored-by: LocalAI [bot] <localai-bot@users.noreply.github.com>