feat: Integrate ASP.NET Core Identity for user authentication

This commit integrates ASP.NET Core Identity into the application to enable user registration, login, and management. This lays the groundwork for securing data per user.

**Key Changes:**

*   **DbContext Configuration:**
    *   Modified `ApplicationDbContext.cs` to inherit from `IdentityDbContext<IdentityUser>`.
    *   Removed an unnecessary `using` statement from `ApplicationDbContext.cs`.

*   **Program.cs Setup:**
    *   Configured `AddDefaultIdentity<IdentityUser>` with `AddEntityFrameworkStores<ApplicationDbContext>()` to register Identity services.
    *   Ensured correct ordering of `UseAuthentication()` and `UseAuthorization()` middleware.
    *   Added `app.MapRazorPages()` to enable the Identity UI pages.
    *   Verified core package versions in `turf_tasker.csproj` for consistency across EF Core and Identity components (`8.0.6`).

*   **Identity UI:**
    *   Scaffolded ASP.NET Core Identity pages (Login, Register, Manage, etc.) to provide the user interface for authentication.
    *   Added a `_LoginPartial.cshtml` partial view to the `Views/Shared` folder.
    *   Rendered `_LoginPartial` in `Views/Shared/_Layout.cshtml` to display login/register/logout links in the navigation bar.

*   **Migrations:**
    *   Created and applied a new migration (`AddIdentitySchema`) to create the necessary ASP.NET Core Identity database tables (e.g., `AspNetUsers`, `AspNetRoles`).

Areas/Identity/Pages/Account/Manage/_Layout.cshtml

@@ -0,0 +1,29 @@
+@{
+    if (ViewData.TryGetValue("ParentLayout", out var parentLayout) && parentLayout !=  null)
+    {
+        Layout = parentLayout.ToString();
+    }
+    else
+    {
+        Layout = "/Areas/Identity/Pages/_Layout.cshtml";
+    }
+}
+
+<h1>Manage your account</h1>
+
+<div>
+    <h2>Change your account settings</h2>
+    <hr />
+    <div class="row">
+        <div class="col-md-3">
+            <partial name="_ManageNav" />
+        </div>
+        <div class="col-md-9">
+            @RenderBody()
+        </div>
+    </div>
+</div>
+
+@section Scripts {
+    @RenderSection("Scripts", required: false)
+}