Refactor AutoMerge.Standalone to reuse shared AutoMerge changeset and branch pipelines

[Copilot]

The new standalone app carried duplicate changeset retrieval/mapping logic instead of reusing the existing AutoMerge implementation. This PR moves standalone onto shared providers/models and exposes only the minimum shared surface needed for that reuse.

• Shared provider reuse in standalone

  • AutoMerge.Standalone/AutoMergeControl.cs now uses:
    • MyChangesetChangesetProvider for recent changesets
    • ChangesetByIdChangesetProvider for add-by-id
    • ChangesetViewModel as the shared data model
  • Removed standalone-local changeset query/mapping duplication.

• Shared branch discovery reuse in standalone

  • AutoMergeControl now retrieves branches for the selected changeset using the same branch discovery path as the main project.
  • BranchesViewModel.GetBranches(...) was made reusable and is now used by both:
    • BranchesViewModel.RefreshAsync() in the main project
    • AutoMergeControl.UpdateBranchesViewAsync() in standalone
  • Standalone branch list now shows source/target classification and validation messages from shared branch logic.

• Provider extensibility for non-Team Explorer hosts

  • Added ChangesetProviderBase(ChangesetService, string projectName) path for direct service injection.
  • Added matching overloads in:
    • MyChangesetChangesetProvider
    • ChangesetByIdChangesetProvider
  • Existing IServiceProvider-based behavior remains unchanged.

• Minimal visibility change to enable reuse

  • Settings changed from internal to public so standalone can consume shared settings (e.g., ChangesetCount).

var provider = new MyChangesetChangesetProvider(
    _changesetService,
    "Intact iQ",
    Settings.Instance.ChangesetCount);

_changesets = await provider.GetChangesets(_versionControl.AuthorizedUser);

[vbtrek]

@copilot This is quite a good first attempt, in UpdateBranchesView() in AutoMergeControl we need to retrieve the branches for the selected changeset, this seems to be done by BranchesViewModel.RefreshAsync() in the main project

[Copilot]

@copilot This is quite a good first attempt, in UpdateBranchesView() in AutoMergeControl we need to retrieve the branches for the selected changeset, this seems to be done by BranchesViewModel.Refresh...

Implemented in 59cc702.

AutoMergeControl now loads branches for the selected changeset via shared BranchesViewModel.GetBranches(...) logic (same discovery path used by the main project), including source/target classification and validation message display.