web: add basic ASP.NET Core web interface

PluralKit.Web/Pages/ViewSystem.cshtml.cs

@@ -0,0 +1,32 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace PluralKit.Web.Pages
+{
+    public class ViewSystem : PageModel
+    {
+        private SystemStore _systems;
+        private MemberStore _members;
+
+        public ViewSystem(SystemStore systems, MemberStore members)
+        {
+            _systems = systems;
+            _members = members;
+        }
+        
+        public PKSystem System { get; set; }
+        public IEnumerable<PKMember> Members { get; set; }
+
+        public async Task<IActionResult> OnGet(string systemId)
+        {
+            System = await _systems.GetByHid(systemId);
+            if (System == null) return NotFound();
+
+            Members = await _members.GetBySystem(System);
+
+            return Page();
+        }
+    }
+}