feat(scale): g→ml density conversion for liquid products

- _scaleDensityForProduct(): returns g/ml density based on product name/category
  olio oliva 0.91, girasole 0.92, spirits 0.94, aceto/panna 1.01, latte 1.03,
  yogurt 1.05, succo 1.04, miele/sciroppo 1.40, default 1.00 (water)
- _scaleAutoFillUse(): normalises all scale units to grams first, then converts
  to target unit; when unit=ml applies density; never touches pz/conf

index.html

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-<script src="assets/js/app.js?v=20260415d"></script>
+<script src="assets/js/app.js?v=20260415e"></script>
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