Document editor and simulation code

[wnj00524]

Refresh the README to match the current in-app editing workflow and add explanatory comments and XML documentation across the public models, services, and key view-model logic.

[gemini-code-assist]

Code Review

This pull request adds comprehensive XML documentation and internal comments to the network simulator's models, services, and view models to improve code maintainability. It also updates the README with an "Editing In App" guide and a "Code Structure" overview. Feedback was provided to correct absolute local file paths in the README links to relative paths to ensure they work for all users.

[gemini-code-assist]

The links in the 'Code Structure' section use absolute file paths specific to your local environment (e.g., /C:/Users/...). These links will not function correctly for other users or within the repository's hosting environment. Please use relative paths starting from the repository root.

Suggested change

	- [MainWindow.xaml](/C:/Users/jdwil/source/repos/Codex/MedWNetworkSim/src/MedWNetworkSim.App/MainWindow.xaml) defines the main shell: canvas, summary panes, simulation results, and the in-app editor grids.
	- [MainWindowViewModel.cs](/C:/Users/jdwil/source/repos/Codex/MedWNetworkSim/src/MedWNetworkSim.App/ViewModels/MainWindowViewModel.cs) is the application coordinator. It loads/saves networks, keeps editor selections in sync, and triggers simulation.
	- [NodeEditorWindow.xaml](/C:/Users/jdwil/source/repos/Codex/MedWNetworkSim/src/MedWNetworkSim.App/NodeEditorWindow.xaml) provides the dedicated dropdown-driven node editing workflow.
	- [NetworkFileService.cs](/C:/Users/jdwil/source/repos/Codex/MedWNetworkSim/src/MedWNetworkSim.App/Services/NetworkFileService.cs) normalizes and validates JSON data and applies automatic layout.
	- [NetworkSimulationEngine.cs](/C:/Users/jdwil/source/repos/Codex/MedWNetworkSim/src/MedWNetworkSim.App/Services/NetworkSimulationEngine.cs) performs routing, capacity competition, bid-cost calculation, and consumer-cost summarization.
	- [MainWindow.xaml](src/MedWNetworkSim.App/MainWindow.xaml) defines the main shell: canvas, summary panes, simulation results, and the in-app editor grids.
	- [MainWindowViewModel.cs](src/MedWNetworkSim.App/ViewModels/MainWindowViewModel.cs) is the application coordinator. It loads/saves networks, keeps editor selections in sync, and triggers simulation.
	- [NodeEditorWindow.xaml](src/MedWNetworkSim.App/NodeEditorWindow.xaml) provides the dedicated dropdown-driven node editing workflow.
	- [NetworkFileService.cs](src/MedWNetworkSim.App/Services/NetworkFileService.cs) normalizes and validates JSON data and applies automatic layout.
	- [NetworkSimulationEngine.cs](src/MedWNetworkSim.App/Services/NetworkSimulationEngine.cs) performs routing, capacity competition, bid-cost calculation, and consumer-cost summarization.