Update Italian datepicker locale: replace weekHeader "Sm" with "#"

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• “Sm” (“Settimana”) is not a common or standardized abbreviation for week numbering in Italian.
• Italian UI/UX patterns typically do not use a short form like “Sm” in calendars.
• Many Italian applications and internationalized UIs use “#” as a neutral and widely recognizable symbol for numbered columns, matching how Italians often represent “numero” (e.g. “n°”, “#”).
• Using “#” aligns better with common calendar implementations in Italian enterprise and technical software, improving clarity and reducing ambiguit