Fix ArgumentOutOfRangeException crash in Problems list

[hendrikmennen]

Problem

The app crashes with:

System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values. (Parameter 'index')
   at Avalonia.Collections.DataGridCollectionView.GetItemAt(Int32 index)
   at Avalonia.Collections.DataGridCollectionView.get_IsCurrentInSync()
   at Avalonia.Collections.DataGridCollectionView.AdjustCurrencyForRemove(Int32 index)
   at Avalonia.Collections.DataGridCollectionView.ProcessRemoveEvent(Object removedItem, Boolean isReplace)
   at Avalonia.Collections.DataGridCollectionView.ProcessCollectionChanged(NotifyCollectionChangedEventArgs args)
   at System.Collections.ObjectModel.ObservableCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   at OneWare.AI.UI.ViewModels.AiProjectViewModel.RefreshDiagnostics(Boolean includeExpensiveChecks)

Root cause

Upstream bug in Avalonia's DataGridCollectionView: ProcessRemoveEvent does not check PassesFilter (unlike ProcessAddEvent).

When an item that is filtered out of the view is removed from the source collection:

1. removeIndex = IndexOf(removedItem) is -1
2. needToRemove is still true (internalRemoveIndex < (PageIndex + 1) * PageSize → -1 < 0)
3. AdjustCurrencyForRemove(-1) takes the index < CurrentPosition branch and does SetCurrent(CurrentItem, CurrentPosition - 1) → CurrentPosition == -1 while CurrentItem is still in the view
4. The CurrentPosition >= Count guard doesn't catch a negative position
5. IsCurrentInSync → IsCurrentInView is true → GetItemAt(-1) throws

So it reproduces whenever a problem row at position 0 is current and a filtered-out error is removed — exactly what IErrorService.RefreshErrors does during an AI project diagnostics refresh.

Fix

Added BatchObservableCollection<T>, which suppresses change notifications while a batch of mutations is applied and raises a single Reset afterwards. DataGridCollectionView handles Reset via RefreshOrDefer() → RefreshOverride(), which rebuilds the view and restores currency through ResetCurrencyValues, bypassing the broken incremental-remove path entirely.

All removal paths in ErrorListViewModel are now batched: RefreshErrors, ClearFile, Clear(source), Clear(project) and Clear(project, source). No Reset is raised if the batch didn't actually change anything, so unchanged diagnostics refreshes stay free.

Verification

Standalone repro against Avalonia.Controls.DataGrid:

before: cur=b pos=0
plain CRASH: ArgumentOutOfRangeException Specified argument was out of the range of valid values. (Parameter 'index')
batch: no crash, count=2 cur=b pos=0

The batched collection completes cleanly and preserves the current item/position. dotnet build src/OneWare.ErrorList/OneWare.ErrorList.csproj succeeds with 0 errors.