- Fix scale bar checkbox: replace shadcn Checkbox (broken event
propagation) with native input[type=checkbox] + v-model
- Scale input: use local string ref so user can type freely;
red highlight when invalid, run button disabled until valid
- Auto-compute default scale to match input image dimensions,
capped at 8192px output; cached scale takes priority
Co-Authored-By: Claude <noreply@anthropic.com>
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