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/session-log.ts

@@ -1,4 +1,5 @@
 import fs from "node:fs";
+import { logTimestamp } from "./log-timestamp";
 import path from "node:path";
 import { setLogListener } from "./logger";
 
@@ -86,7 +87,7 @@ export function initSessionLog(baseDir: string): void {
   const timestamp = formatTimestamp();
   sessionLogPath = path.join(sessionLogsDir, `session_${timestamp}.txt`);
 
-  const isoTimestamp = new Date().toISOString();
+  const isoTimestamp = logTimestamp();
   try {
     fs.writeFileSync(sessionLogPath, `=== Session gestartet: ${isoTimestamp} ===\n`, "utf8");
   } catch {
@@ -116,7 +117,7 @@ export function shutdownSessionLog(): void {
   flushPending();
 
   // Write closing line
-  const isoTimestamp = new Date().toISOString();
+  const isoTimestamp = logTimestamp();
   try {
     fs.appendFileSync(sessionLogPath, `=== Session beendet: ${isoTimestamp} ===\n`, "utf8");
   } catch {