Datenbank sichern: Backup als .tar.gz mit Server-Ablage und Client-Download

- Neuer POST /api/backup Endpoint (BackupEndpoint.cs)
- Packt gott.db in data/backup/gott-{timestamp}.tar.gz
- Gibt Archiv gleichzeitig als Download an Client zurück
- Button 'Datenbank sichern' im Header-Dropdown-Menü
- Content-Disposition Header-Parsing mit filename* UTF-8 Support

Endpoints/BackupEndpoint.cs

@@ -0,0 +1,55 @@
+using System;
+using System.Diagnostics;
+using System.IO;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Routing;
+
+namespace Gott.Endpoints;
+
+public static class BackupEndpoint
+{
+    public static void MapBackupEndpoint(this IEndpointRouteBuilder app)
+    {
+        app.MapPost("/api/backup", HandleBackup);
+    }
+
+    private static async System.Threading.Tasks.Task<IResult> HandleBackup()
+    {
+        var dataDir = Path.Combine(AppContext.BaseDirectory, "data");
+        var dbPath = Path.Combine(dataDir, "gott.db");
+
+        if (!File.Exists(dbPath))
+            return Results.NotFound(new { error = "Datenbank nicht gefunden" });
+
+        var backupDir = Path.Combine(dataDir, "backup");
+        Directory.CreateDirectory(backupDir);
+
+        var timestamp = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
+        var archiveName = $"gott-{timestamp}.tar.gz";
+        var archivePath = Path.Combine(backupDir, archiveName);
+
+        var psi = new ProcessStartInfo
+        {
+            FileName = "tar",
+            ArgumentList = { "-czf", archivePath, "-C", dataDir, "gott.db" },
+            RedirectStandardError = true,
+            UseShellExecute = false
+        };
+
+        using (var process = Process.Start(psi))
+        {
+            if (process == null)
+                return Results.StatusCode(500);
+
+            var stderr = await process.StandardError.ReadToEndAsync();
+            await process.WaitForExitAsync();
+
+            if (process.ExitCode != 0)
+                return Results.Problem($"tar fehlgeschlagen: {stderr}");
+        }
+
+        var bytes = await File.ReadAllBytesAsync(archivePath);
+        return Results.File(bytes, "application/gzip", archiveName);
+    }
+}