Refactor application structure and add database support

Changed App.xaml.cs to implement dependency injection with Microsoft.Extensions.Hosting, initializing services for LandingWindow and LandingViewModel.

Removed MainWindow.xaml and MainWindow.xaml.cs, shifting to a new landing window structure.

Added Ghost.Database project with necessary database functionality and created ProjectRepository for project management.

Added ProjectInfo and TemplateInfo data models for project attributes.

Added CreateProjectViewModel and LandingViewModel for managing view models using Community Toolkit for MVVM.

Created new XAML pages for project creation, opening projects, and the landing window, along with their corresponding code-behind files.

Added AssemblyInfo.cs for internal visibility to facilitate testing.

Ghost.Editor/View/Windows/LandingWindow.xaml

@@ -0,0 +1,40 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<Window
+    x:Class="Ghost.Editor.View.Windows.LandingWindow"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+    xmlns:local="using:Ghost.Editor.View.Windows"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    Title="Landing"
+    mc:Ignorable="d">
+
+    <Grid Padding="4">
+        <Grid.RowDefinitions>
+            <RowDefinition Height="Auto" />
+            <RowDefinition Height="*" />
+        </Grid.RowDefinitions>
+
+        <SelectorBar
+            Grid.Row="0"
+            HorizontalAlignment="Right"
+            SelectionChanged="SelectorBar_SelectionChanged">
+            <SelectorBarItem IsSelected="True" Text="Open">
+                <SelectorBarItem.Icon>
+                    <FontIcon Glyph="&#xE8A7;" />
+                </SelectorBarItem.Icon>
+            </SelectorBarItem>
+            <SelectorBarItem Text="Create">
+                <SelectorBarItem.Icon>
+                    <FontIcon Glyph="&#xE8F4;" />
+                </SelectorBarItem.Icon>
+            </SelectorBarItem>
+        </SelectorBar>
+
+        <Frame
+            x:Name="ContentFrame"
+            Grid.Row="1"
+            Padding="24,8"
+            IsNavigationStackEnabled="False" />
+    </Grid>
+</Window>