feat: Settings in Datenbank speichern statt localStorage

- Neue Spalte 'settings' in users-Tabelle (Migration via TryAddColumn)
- SettingsEndpoint: GET/PUT /api/settings
- DatabaseService: GetUserSettings() + UpdateUserSettings()
- Frontend: currentSettings als globaler State in app.js
- settings-page.js: localStorage komplett entfernt, nutzt API
- Settings werden beim App-Start aus DB geladen und angewendet

Endpoints/SettingsEndpoint.cs

@@ -0,0 +1,35 @@
+using System.Text.Json;
+using Gott.Extensions;
+using Gott.Services;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Routing;
+
+namespace Gott.Endpoints;
+
+public static class SettingsEndpoint
+{
+    public static void MapSettingsEndpoints(this WebApplication app)
+    {
+        app.MapGet("/api/settings", HandleGet);
+        app.MapPut("/api/settings", HandleUpdate);
+    }
+
+    private static async System.Threading.Tasks.Task HandleGet(HttpContext ctx, DatabaseService db)
+    {
+        var userId = ctx.GetUserId();
+        var json = await db.GetUserSettings(userId);
+        ctx.Response.ContentType = "application/json";
+        await ctx.Response.WriteAsync(json ?? "{}");
+    }
+
+    private static async System.Threading.Tasks.Task HandleUpdate(HttpContext ctx, DatabaseService db)
+    {
+        var userId = ctx.GetUserId();
+        var body = await JsonSerializer.DeserializeAsync<JsonElement>(ctx.Request.Body);
+        var json = body.ToString();
+        await db.UpdateUserSettings(userId, json);
+        ctx.Response.ContentType = "application/json";
+        await ctx.Response.WriteAsync(json);
+    }
+}