swiftui-conventionslisted

## Purpose Consistent SwiftUI patterns across the codebase — predictable state management and view composition. ## Checklist - **@State**: for simple value-type state owned by a single view (toggles, text field values, expand/collapse). - **@Binding**: for child views that need to read/write a parent's state. Prefer binding to a specific field, not the entire model. - **@StateObject**: for reference-type view models owned by this view. The view that creates the model owns it with `@StateObject`. - **@ObservedObject**: for view models passed in from a parent. Never use `@ObservedObject` to create a model — that's `@StateObject`'s job. - **@EnvironmentObject**: for app-wide dependencies (auth state, theme, data store). Use sparingly — prefer explicit passing for most cases. - **View composition**: extract reusable subviews into computed properties or small `View` structs. Use `@ViewBuilder` for conditional content. - **Previews**: every view has a preview provider showing default state, empty state, and error state. ## Expected output SwiftUI views with predictable state management, no business logic in views, and preview coverage for all states.