add extension func

[JusterZhu]

No description provided.

[JusterZhu]

@copilot Fully understand the code in the current PR, optimize the code as a whole, and ensure that the functions work properly and can be put into practical use.

[Copilot]

@JusterZhu I've opened a new pull request, #6, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

Pull request overview

Adds a new “Extension” tab to the Avalonia tool UI intended to configure and build an extension package (zip + manifest), including new view/viewmodel and supporting models/utilities.

Changes:

• Add ExtensionView UI and wire it into MainWindow as a new tab.
• Introduce ExtensionViewModel + config/models for extension manifest/custom properties.
• Add ZipUtility helper for zip compression/extraction and zip mutation.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
src/Views/MainWindow.axaml	Adds the new “Extension” tab and switches existing view tags to self-closing form.
src/Views/ExtensionView.axaml.cs	New view code-behind for ExtensionView.
src/Views/ExtensionView.axaml	New UI for extension metadata, custom properties, and build/clear actions.
src/ViewModels/ExtensionViewModel.cs	Implements extension package generation and UI commands/state.
src/Models/TargetPlatform.cs	Adds a flagged enum for platform targeting.
src/Models/ExtensionDependencySelectionModel.cs	Adds a model for (future) dependency selection.
src/Models/ExtensionConfigModel.cs	Adds the extension manifest/config model bound to the UI.
src/Models/CustomPropertyModel.cs	Adds a model for displaying custom properties in the UI list.
src/Common/ZipUtility.cs	Adds zip compression/extraction helpers and manifest insertion support.

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