feat: enhance navigation and UI structure in MainView and Application. (#811)

* feat: enhance navigation and UI structure in MainView and Application.

* feat: implement singleton pattern for PaletteDemoViewModel and add initialization check

* feat: set FontWeight to Normal for navigation button in MainView

---------

Co-authored-by: Dong Bin <popmessiah@hotmail.com>

.github/COMMIT_CONVENTION.md

@@ -0,0 +1,92 @@
+# Git Commit Message Convention
+
+This project follows the [Conventional Commits](https://www.conventionalcommits.org/) specification for commit messages.
+
+## Format
+
+```
+<type>[optional scope]: <description>
+
+[optional body]
+
+[optional footer(s)]
+```
+
+## Types
+
+| Type | Description |
+|------|-------------|
+| `feat` | A new feature |
+| `fix` | A bug fix |
+| `docs` | Documentation only changes |
+| `style` | Changes that do not affect the meaning of the code (formatting, missing semicolons, etc.) |
+| `refactor` | A code change that neither fixes a bug nor adds a feature |
+| `perf` | A code change that improves performance |
+| `test` | Adding missing tests or correcting existing tests |
+| `build` | Changes that affect the build system or external dependencies |
+| `ci` | Changes to CI configuration files and scripts |
+| `chore` | Other changes that don't modify source or test files |
+| `revert` | Reverts a previous commit |
+
+## Rules
+
+1. **Limit the subject line to 50 characters** (72 character hard limit)
+2. **Use the imperative mood** in the subject line (e.g., "add feature" not "added feature")
+3. **Do not end the subject line with a period**
+4. **Use lowercase** for the description (e.g., "add feature" not "Add feature")
+5. **Separate subject from body with a blank line**
+6. **Wrap the body at 72 characters**
+7. **Use the body to explain what and why**, not how
+8. **Reference issues and pull requests** in the footer
+
+## Scope
+
+The scope should be the name of the package or area affected (e.g., `button`, `datepicker`, `theme`, `demo`).
+
+## Examples
+
+### Simple commit
+
+```
+feat(button): add loading state support
+```
+
+### Commit with body
+
+```
+fix(datepicker): correct month navigation overflow
+
+When navigating past December, the month index wrapped to a
+negative value instead of rolling over to January of the next year.
+```
+
+### Commit with breaking change
+
+```
+feat(theme)!: rename SemiColorPrimary to SemiColorBrand
+
+BREAKING CHANGE: The token SemiColorPrimary has been renamed to
+SemiColorBrand. Update all references in your custom theme files.
+```
+
+### Commit referencing an issue
+
+```
+fix(textbox): placeholder not visible in dark mode
+
+Closes #123
+```
+
+## Breaking Changes
+
+Breaking changes must be indicated by appending a `!` after the type/scope, or by including a `BREAKING CHANGE:` footer. Both methods may be used together.
+
+## Revert Commits
+
+When reverting a previous commit, use the `revert` type and reference the reverted commit SHA in the footer:
+
+```
+revert: feat(button): add loading state support
+
+Revert commit a1b2c3d.
+```

demo/Semi.Avalonia.Demo/Pages/PaletteDemo.axaml.cs

@@ -12,14 +12,16 @@ public partial class PaletteDemo : UserControl
     public PaletteDemo()
     {
         InitializeComponent();
-        this.DataContext = new PaletteDemoViewModel();
+        this.DataContext = PaletteDemoViewModel.Instance.Value;
     }
 
     protected override async void OnApplyTemplate(TemplateAppliedEventArgs e)
     {
         base.OnApplyTemplate(e);
-        PaletteDemoViewModel? vm = this.DataContext as PaletteDemoViewModel;
+        if (this.DataContext is PaletteDemoViewModel vm && !vm.IsInitialized)
-        await Dispatcher.UIThread.InvokeAsync(() => { vm?.InitializeResources(); });
+        {
+            await Dispatcher.UIThread.InvokeAsync(() => { vm?.InitializeResources(); });
+        }
     }
 
     public async Task Copy(object? o)
@@ -31,4 +33,4 @@ public partial class PaletteDemo : UserControl
             await c.SetTextAsync(o.ToString());
         }
     }
-}
+}

demo/Semi.Avalonia.Demo/ViewModels/PaletteDemoViewModel.cs

@@ -14,6 +14,8 @@ namespace Semi.Avalonia.Demo.ViewModels;
 
 public partial class PaletteDemoViewModel : ObservableObject
 {
+    public static Lazy<PaletteDemoViewModel> Instance { get; } = new(() => new PaletteDemoViewModel());
+    public bool IsInitialized { get; private set; }
     private readonly string[] _predefinedColorNames =
     [
         "Red", "Pink", "Purple", "Violet", "Indigo",
@@ -44,6 +46,7 @@ public partial class PaletteDemoViewModel : ObservableObject
         InitializePalette();
         InitializeFunctionalColors();
         InitializeShadows();
+        IsInitialized = true;
     }
 
     private void InitializePalette()
@@ -289,4 +292,4 @@ public partial class ShadowGroupViewModel : ObservableObject
             }
         }
     }
-}
+}

demo/Semi.Avalonia.Demo/Views/MainView.axaml

@@ -83,6 +83,7 @@
                                                 <Border Classes="NavItemHost" Classes.Selected="{Binding IsSelected}">
                                                     <Button
                                                         Classes="NavItem"
+                                                        FontWeight="Normal"
                                                         Classes.Selected="{Binding IsSelected}"
                                                         Command="{Binding NavigateCommand}"
                                                         CommandParameter="{Binding}"