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Refactor app shell into MVVM layers and enforce architecture boundaries #353

Job	Run time
Shell Deploy Scripts	13s
Rust Build Check (windows-latest)	8m 34s
CLI Tests (macos-15)	13m 32s
Rust Build Check (macos-15)	4m 15s
Rust Build Check (ubuntu-latest)	4m 59s
Frontend Build	34s
CLI Tests (ubuntu-latest)	1m 12s
	33m 19s