[DevMando]

Summary

Desktop's Controls, Services, and MainWindow files were spread across long, flat file lists. This PR groups related files into folders so contributors can find a feature's UI and supporting code more easily.

The application keeps the same UI and behavior. All 125 moved source files are unchanged; Git recognizes them as 100% identical renames.

What changed

• Controls: group 26 files into Chat, Common, Notes, Settings, and Terminal. Keep each XAML control, its code-behind, and its partial files together.
• Services: group 81 files by responsibility, including agents, AI, approvals, browser tools, configuration, input, notes, project information, rendering, sessions, snapshots, terminal, appearance, workspaces, music, and diagnostics.
• MainWindow: move 18 files under MainWindow. Keep the window XAML and startup/shutdown code-behind together, with partial files under Agents, Navigation, Panels, Settings, and Shared.
• Build references: update direct service-source links in the unit-test and browser smoke-test projects. Correct the browser harness's stale reference to the engine's ProjectRootAccessor location.
• Contributor guidance: add folder guides and update the architecture documentation, background-assets guide, and Unreleased changelog.

Existing namespaces, XAML class names, and MainWindow's partial-class structure are preserved. The folders organize existing responsibilities without changing which objects own state.

Why this was done

As Desktop has grown, finding related files has become harder. For example, all ChatTabView files now live together under Controls/Chat, while workspace state and layout helpers live under Services/Workspaces. The folder guides give future additions a clear home.

How it was tested

• Release Desktop build passed with zero warnings and errors.
• All 604 Desktop tests passed in Release.
• Release browser smoke-test harness build passed with zero warnings and errors. The interactive browser scenarios were not rerun.
• Verified the contents of all 125 moved source files against their original versions; none changed.
• Patch whitespace checks passed.

The final Release checks used Desktop's currently pinned engine revision, so this PR can merge independently of CLI PR #136.

Notes

This PR does not change dependencies, application version, or the engine submodule pin. The separate CLI component reorganization and local engine launch-settings edit are excluded.