fix: correct shelf lives, prawn data and step texts of the new recipes

[guplem]

Fixes the data errors that a review found in the 29 recipes from #71. It also fixes the Mercadona guide that caused two of them.

Data fixes (RecipeBook.tsr)

• Gambas con queso: the recipe put 250 g of salt per serving on the shopping list. The salt is a cooking crust that you throw away, so it is now only in the step text.

• Gambas: the product is peeled frozen prawns, but the steps said to peel them and keep the heads. The steps now thaw them instead. gramsPerPiece changes from 20 to 12, the weight of a medium peeled prawn.

• Jamón cocido: the opened shelf life changes from 5 to 2 days. Mercadona says 48 hours.

• Coco rallado: the opened shelf life is now 7 days. Mercadona says one week.

• Sealed shelf life (shelfLifeDaysClosed) was missing for chilled and frozen items, so the app never warned that they may expire. The new values follow the older similar ingredients:

  Ingredient	Days
  Jamón cocido	21
  Chistorra	14
  Queso en lonchas para fundir	45
  Quesitos en porciones	90
  Mantequilla	90
  Almejas	365
  Gambas	365

  Jamón cocido and Chistorra also get canBeFrozen, like the other deli meats.

• Garlic text: "Ajo troceado" is chopped garlic. Lentejas, Gambas al ajillo and Dorada al horno described whole or sliced cloves, and Lentejas even took the garlic out after cooking. The texts now match chopped garlic.

• Revuelto de setas: "4 partes del aceite" now says "dos tercios del aceite", which is what the booklet means.

Doc fix (mercadona-api.md)

• The guide now says to read both storage_instructions and usage_instructions. The opened shelf life is often only in the second field.
• The guide now says to use drained_weight when unit_size is null.

Not changed

Some booklet portions are small: 62.5 g of pasta, 1-egg tortillas and 1 salmon piece per serving. Some total times are longer than the booklet. These were left as they are on purpose.

Testing

flutter test test/: all 1053 tests pass.

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