fix(ci): use BMP3 format and generate icon.ico for NSIS installer

[ClausValcaTD]

Uses BMP3 format prefix for ImageMagick installer image outputs and generates assets/icons/icon.ico from icon.png for the NSIS installer build step in Release.yml.

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PR created automatically by Jules for task 4711931465959543900 started by @ClausValcaTD

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