Fix: Log-Zeitstempel in lokaler Zeit (mit Offset) statt UTC

User-Report: Logs zeigten z.B. "17:29:43" obwohl es lokal 19:29:43 war (CEST/UTC+2), weil
alle Logger `new Date().toISOString()` (UTC "...Z") nutzten. Neuer Helper logTimestamp()
formatiert lokale Zeit mit explizitem Offset (ISO 8601, z.B. "2026-05-31T19:29:43.605+02:00")
— menschlich lokal UND weiterhin eindeutig/Date.parse-bar. Angewandt auf alle Log-Zeilen-
Writer: item-log, logger (rd_downloader.log), audit-log, rename-log, session-log,
package-log, account-rotation-log, trace-log. Interne/API-/Dateinamen-Zeitstempel
(debug-server, support-bundle, trace autoDisableAt-Config) bleiben absichtlich UTC.

Test: tests/log-timestamp.test.ts (Format + Round-Trip zum selben Instant + lokale Stunde,
TZ-unabhaengig). 650 Tests gruen, tsc 9, Build sauber.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/main/audit-log.ts

@@ -1,4 +1,5 @@
 import fs from "node:fs";
+import { logTimestamp } from "./log-timestamp";
 import path from "node:path";
 
 type AuditLevel = "INFO" | "WARN" | "ERROR";
@@ -78,7 +79,7 @@ export function initAuditLog(baseDir: string): void {
     if (!fs.existsSync(auditLogPath)) {
       fs.writeFileSync(auditLogPath, "", "utf8");
     }
-    fs.appendFileSync(auditLogPath, `=== Audit-Log Start: ${new Date().toISOString()} ===\n`, "utf8");
+    fs.appendFileSync(auditLogPath, `=== Audit-Log Start: ${logTimestamp()} ===\n`, "utf8");
   } catch {
     auditLogPath = null;
   }
@@ -95,7 +96,7 @@ export function logAuditEvent(level: AuditLevel, message: string, fields?: Recor
     }
     fs.appendFileSync(
       auditLogPath,
-      `${new Date().toISOString()} [${level}] ${message}${formatFields(fields)}\n`,
+      `${logTimestamp()} [${level}] ${message}${formatFields(fields)}\n`,
       "utf8"
     );
   } catch {
@@ -115,7 +116,7 @@ export function shutdownAuditLog(): void {
     return;
   }
   try {
-    fs.appendFileSync(auditLogPath, `=== Audit-Log Ende: ${new Date().toISOString()} ===\n`, "utf8");
+    fs.appendFileSync(auditLogPath, `=== Audit-Log Ende: ${logTimestamp()} ===\n`, "utf8");
   } catch {
     // ignore
   }