Fix looping error when movie/series is deleted from another device

[Copilot]

When a movie/series detail view is open and the item is deleted from another device, onBecomeActive triggers reload() → API returns 404 → error alert shown. On macOS, dismissing the alert re-activates the window (appearsActive toggles), firing onBecomeActive again — infinite loop.

Changes

• API.Error.isNotFound — new computed property matching badStatusCode(404) and errorResponse(404, _)
• Movies / SeriesModel .get operation — on 404, remove the item from local items before re-throwing, keeping local cache consistent
• MovieView / SeriesDetailView / SeasonView reload() — on 404, clear the error and reset the navigation path to root

// before
func reload() async {
    _ = await instance.movies.get(movie)
}

// after
func reload() async {
    guard await instance.movies.get(movie) else {
        if instance.movies.error?.isNotFound == true {
            instance.movies.error = nil
            dependencies.router.moviesPath = .init()
        }
        return
    }
}

Navigation resets to root (not removeLast()) since the detail view may have child views pushed on the stack, and onBecomeActive fires for all views in the macOS window hierarchy simultaneously.

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