Stufe 1 (#764): Werkzeugeinstellungen, Sicherungszeitplan und Import als neue Instanz

- Werkzeugformulare aus den typisierten Einstellungsklassen (L8): Geheimnisse
  nur schreibend, nur geaenderte Schluessel werden ersetzt, Rechte bleiben
- Database.allowedTables las ein JSON-Array als rohen Text und haette es beim
  naechsten Speichern zerlegt
- Automatische Sicherung der Instanz in der Sicherungsansicht (L10)
- Sicherung hochladen und als neue Instanz einspielen (L11): Pfade der alten
  Maschine werden zurueckgesetzt, eine Kopie neben dem Original bekommt eine
  eigene ID, Autostart aus; Upload bis 4 GB
- api.js schickte eine Datei als "{}"; Dialoge schliessen beim Seitenwechsel

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ClawdDotNet.Manager.Web/Endpoints.cs

@@ -102,6 +102,12 @@ public sealed record ManagerSettingsUpdateDto(string? DeploymentcenterUrl, strin
 /// </summary>
 internal static class ManagerEndpoints
 {
+    /// <summary>
+    /// #764: Upper limit for an uploaded backup. Kestrel's default of 30 MB is far below a
+    /// backup with chat histories and state.db; without a limit, an upload could fill the disk.
+    /// </summary>
+    private const long MaxImportBytes = 4L * 1024 * 1024 * 1024;
+
     // ─── Was den Manager selbst angeht ───
 
     public static void MapVerwaltung(this WebApplication app)
@@ -382,6 +388,57 @@ internal static class ManagerEndpoints
             }
         });
 
+        // ─── Import a backup as a new instance (#764) ───
+        //
+        // The file comes as the raw request body, not as a form: the access token is a header,
+        // not a cookie, so there is no cross-site form to guard against, and a raw body needs
+        // no antiforgery exception. The source license key travels in a header and never in
+        // the address, where it would end up in logs.
+        verwaltung.MapPost("/backups/import", async (
+            HttpContext context, ManagerBackups backups, CancellationToken ct) =>
+        {
+            var name = context.Request.Query["name"].ToString();
+            if (string.IsNullOrWhiteSpace(name))
+                return Results.BadRequest(new OutcomeDto(false, "The new instance needs a name."));
+
+            if (context.Features.Get<Microsoft.AspNetCore.Http.Features.IHttpMaxRequestBodySizeFeature>() is { IsReadOnly: false } limit)
+                limit.MaxRequestBodySize = MaxImportBytes;
+
+            var upload = Path.Combine(Path.GetTempPath(), "clawd-import-" + Guid.NewGuid().ToString("N") + ".bin");
+            try
+            {
+                await using (var file = File.Create(upload))
+                    await context.Request.Body.CopyToAsync(file, ct);
+
+                if (new FileInfo(upload).Length == 0)
+                    return Results.BadRequest(new OutcomeDto(false, "The upload was empty."));
+
+                var result = await backups.ImportAsNewInstanceAsync(
+                    upload, name,
+                    context.Request.Headers["X-Source-License-Key"].ToString(),
+                    context.Request.Headers["X-Backup-Passphrase"].ToString(),
+                    CancellationToken.None);
+
+                if (result.KeyNeeded)
+                    return Results.Json(new KeyNeededDto(false, result.Message, "fremde_lizenz"),
+                        statusCode: StatusCodes.Status422UnprocessableEntity);
+
+                return result.Ok
+                    ? Results.Ok(new OutcomeDto(true, result.Message))
+                    : Results.BadRequest(new OutcomeDto(false, result.Message));
+            }
+            catch (Microsoft.AspNetCore.Http.BadHttpRequestException ex) when (ex.StatusCode == StatusCodes.Status413PayloadTooLarge)
+            {
+                return Results.Json(new OutcomeDto(false, $"The backup is larger than {MaxImportBytes / (1024 * 1024 * 1024)} GB."),
+                    statusCode: StatusCodes.Status413PayloadTooLarge);
+            }
+            finally
+            {
+                try { File.Delete(upload); }
+                catch (IOException) { /* temp file; the next cleanup of the temp folder takes it */ }
+            }
+        });
+
         // ─── License and manager settings (#764) ───
 
         verwaltung.MapGet("/license", (ManagerCore manager) =>