fix the tts model dropdown to show the currently selected model

[ErixM]

Description

Ciao! Thanks for this project, it makes everything so easy to run, finally I can fully use my new graphics card!

This PR fixes issues with TTS models not appearing in the UI dropdown and the dropdown not maintaining selection state.

Changes Made

1. Fixed TTS model detection in model_config.go:

   • Removed FLAG_ANY from GetAllModelConfigUsecases() map (line 537) - it was causing false matches due to bitwise operations with value 0
   • Added kokoro and cuda12-kokoro backends to TTS backends list in GuessUsecases() (line 640)

2. Fixed dropdown selection state in tts.html:

   • Moved Alpine.js x-data to parent div and initialized with current model value
   • Changed from x-init watcher to @change event handler for better reactivity

Testing

• Verified TTS models now appear in dropdown at /tts/
• Confirmed dropdown maintains selection when navigating to model-specific pages like /tts/kokoro

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Notes for Reviewers

The main issue was twofold:

1. FLAG_ANY (value 0) in the usecases map caused HasUsecases() to always return true due to bitwise AND operations
2. Kokoro backends weren't recognized as TTS backends in the usecase guessing logic
3. Alpine.js reactive binding wasn't properly initialized with the current model

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• Signed commits

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[mudler]

thanks!