feat: add folder structure option to setup screen

[KasperRagnar]

Summary

• Adds a Structure toggle on the setup screen: Files (default — date-organised images/YYYY/MM/DD/) vs Files & folders (mirrors the phone's original folder hierarchy at the destination)
• Organises the setup screen into labelled sub-sections (File type, Date filter, Structure, Folders) with a visual divider before the path pickers — makes the growing option list easier to scan
• Date filter section is hidden entirely when Files or Music type is selected (previously only partially disabled)
• All new strings translated into English, Danish, and Spanish

Test plan

• Open setup screen — confirm four labelled sections appear with correct spacing
• Select Files or Music file type — confirm the Date filter section disappears entirely
• Select Files & folders and run a transfer — files should land at <dest>/<relative-phone-path>/
• Select Files (default) and run a transfer — files land in <dest>/images/YYYY/MM/DD/ as before
• Switch language to Danish / Spanish — confirm section labels translate correctly
• Click "Back to Start" after a transfer — confirm Structure resets to Files

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