feat(api): redirect root to API docs, return 410 gone for v1 routes

PluralKit.API/Startup.cs

@@ -133,7 +133,15 @@ public class Startup
         app.UseRouting();
         app.UseAuthentication();
         app.UseAuthorization();
-        app.UseEndpoints(endpoints => endpoints.MapControllers());
+        app.UseEndpoints(endpoints =>
+        {
+            // register base / legacy routes
+            endpoints.MapMethods("", new string[] { }, (context) => { context.Response.Redirect("https://pluralkit.me/api"); return Task.CompletedTask;});
+            endpoints.MapMethods("v1/{*_}", new string[] { }, (context) => context.Response.WriteJSON(410, "{\"message\":\"Unsupported API version\",\"code\":0}"));
+
+            // register controllers
+            endpoints.MapControllers();
+        });
 
         // metrics
         app.UseMetricsAllMiddleware();