feat(voice/clone): support MP3 and other audio formats for reference voices (#20)

## Summary
- Adds support for MP3, FLAC, OGG, and other audio formats when
uploading reference voices for cloning
- Replace WAV-only `audio_read()` with a `soundfile`-based
implementation
- Update web UI file picker to accept multiple audio formats

## Changes
- `pocket_tts/data/audio.py`: Use `soundfile` library instead of
Python's `wave` module
- `pocket_tts/main.py`: Preserve original file extension in temp files
for format detection
- `pocket_tts/main.py`: Add missing `truncate=True` to CLI generate
command
- `pocket_tts/static/index.html`: Update file input to accept
`.wav,.mp3,.flac,.ogg,.m4a,audio/*`
- `pyproject.toml`: Add `soundfile>=0.12.0` dependency

## Tested
- [x] Upload a WAV file as reference voice and generate speech
- [x] Upload an MP3 file as reference voice and generate speech
- [x] Upload a FLAC file as reference voice and generate speech
- [x] Verify CLI `--voice` option works with MP3 files

---------

Co-authored-by: Gabriel de Marmiesse <gabrieldemarmiesse@gmail.com>
Co-authored-by: Václav Volhejn <8401624+vvolhejn@users.noreply.github.com>

pocket_tts/static/index.html

@@ -51,16 +51,16 @@
 
         <div class="bg-white p-4 rounded-lg shadow">
             <label for="voice-wav-input" class="block text-sm font-medium text-gray-700 mb-2">
-                Or upload a WAV file for voice cloning:
+                Or upload an audio file for voice cloning:
             </label>
             <input
                 type="file"
                 id="voice-wav-input"
                 class="w-full border rounded p-2"
-                accept=".wav,audio/wav"
+                accept=".wav,.mp3,.flac,.ogg,.m4a,audio/*"
             />
             <p class="text-xs text-gray-500 mt-1">
-                Upload a WAV file to use as voice reference. Takes precedence over voice URL.
+                Upload an audio file (WAV, MP3, FLAC, etc.) to use as voice reference. Takes precedence over voice URL.
             </p>
         </div>