refactor: delete unreachable members and redundant package refs

Eight public members had no caller anywhere in src: GitService.GetFileDiffAsync,
SubtaskRepository.DeleteByTaskIdAsync, TaskRepository.GetByListAsync (a
backwards-compat alias for GetByListIdAsync) and .GetByCreatorAsync,
WorktreeRepository.GetByStatesAsync, TaskMonitorViewModel.SetPendingQuestion
(a duplicate of the live-event lambda), PrimeClaudeTabViewModel.ApplyFiredEvent,
and StreamLineFormatter.FormatFile. TaskAttachmentRepository.DeleteAllForTaskAsync
was reachable only from its own test; the ON DELETE CASCADE on task_attachments
already covers it. Tests for the deleted members go with them.

Dropped two package refs the platform already provides: EntityFrameworkCore.Design
in Worker (the design-time factory and the migrations live in Data, which has its
own ref) and System.IO.FileSystem.AccessControl in Installer.Tests (net8.0-windows
ships the ACL APIs in the shared framework).

tests/ClaudeDo.Installer.Tests/ClaudeDo.Installer.Tests.csproj

@@ -14,7 +14,6 @@
   <ItemGroup>
     <PackageReference Include="coverlet.collector" Version="6.0.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
-    <PackageReference Include="System.IO.FileSystem.AccessControl" Version="5.0.0" />
     <PackageReference Include="xunit" Version="2.5.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.3" />
   </ItemGroup>