feat: Add main application views and structure

- Implemented CreateInstanceView for creating new instances.
- Added HostsView for managing SSH hosts with CRUD operations.
- Created InstancesView for displaying and managing instances.
- Developed LogsView for viewing operation logs.
- Introduced SecretsView for managing secrets associated with hosts.
- Established SettingsView for configuring application settings.
- Created MainWindow as the main application window with navigation.
- Added app manifest and configuration files for logging and settings.

OTSSignsOrchestrator.Core/Migrations/20260218143812_AddAppSettings.cs

@@ -0,0 +1,42 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace OTSSignsOrchestrator.Core.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddAppSettings : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "AppSettings",
+                columns: table => new
+                {
+                    Key = table.Column<string>(type: "TEXT", maxLength: 200, nullable: false),
+                    Value = table.Column<string>(type: "TEXT", maxLength: 4000, nullable: true),
+                    Category = table.Column<string>(type: "TEXT", maxLength: 50, nullable: false),
+                    IsSensitive = table.Column<bool>(type: "INTEGER", nullable: false),
+                    UpdatedAt = table.Column<DateTime>(type: "TEXT", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_AppSettings", x => x.Key);
+                });
+
+            migrationBuilder.CreateIndex(
+                name: "IX_AppSettings_Category",
+                table: "AppSettings",
+                column: "Category");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "AppSettings");
+        }
+    }
+}