fix: tempo slider behavior

[areohbe]

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Summary (optional)

fixes tempo slider behavior when dragging to 0 instead of using reset button. this wa bc of weirdness in svelte if you try to use bind:value with manual change handlers, this just avoids that weirdness entirely.
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Checklist

• Self-reviewed the diff
• Tested locally
• No unrelated changes included

[maxwellmattryan]

Did you test this locally? I pulled in your changes and it 1) became laggy when changing the slider and more importantly 2) stopped playback every time I adjusted the slider.

[areohbe]

Did you test this locally? I pulled in your changes and it 1) became laggy when changing the slider and more importantly 2) stopped playback every time I adjusted the slider.

hmm odd. i did test locally and it was working fine for me. i'll give it another look.