refactor: remove legacy account model and migration util #219

Job	Run time
Prepare CI	1s
Lint App / biomejs	14s
Tests / Run Tests	4m 15s
Build / Build Linux (electron-builder)	3m 40s
Build / Build macOS (electron-builder)	2m 28s
Build / Build Windows (electron-builder)	2m 20s
	12m 58s

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