Fix: Support-Bundle-Export friert die UI nicht mehr 1-2 Minuten ein (asynchrones IO)

buildSupportBundle lief komplett synchron auf dem Electron-Main-Thread:
existsSync/readdirSync/statSync/readFileSync (via AdmZip.addLocalFile) ueber
ALLE Log-Dateien — bei Hunderten item-logs und gleichzeitig laufenden
Downloads (Platte ausgelastet) blockierte das den Event-Loop fuer 1-2 min,
die ganze Oberflaeche stand. Live belegt: ein Bundle mit Hunderten
item-logs-Dateien.

Fix: Alle Datei-Zugriffe im Bundle-Build auf fs.promises (nicht-blockierend)
umgestellt, buildSupportBundle ist jetzt async und liefert Promise<Buffer>.
Dateiinhalte werden per readFile gelesen und mit zip.addFile(buffer)
hinzugefuegt (gleiche Zip-Struktur wie vorher). Der Event-Loop bleibt
waehrend der IO-Wartezeiten frei → UI friert nicht mehr ein. Caller
angepasst (app-controller.exportSupportBundle async, main.ts await,
debug-server via .then).

Test support-bundle.test.ts: valides Zip mit Overview + echter Datei;
ein paralleler Timer feuert waehrend des Builds (Event-Loop nicht blockiert).
840/840 gruen, tsc unveraendert (6), Build ok.

tests/support-bundle.test.ts

@@ -0,0 +1,67 @@
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import AdmZip from "adm-zip";
+import { afterEach, describe, expect, it } from "vitest";
+import { buildSupportBundle } from "../src/main/support-bundle";
+import type { DownloadManager } from "../src/main/download-manager";
+
+const tempDirs: string[] = [];
+
+afterEach(() => {
+  for (const dir of tempDirs.splice(0)) {
+    try { fs.rmSync(dir, { recursive: true, force: true }); } catch {  }
+  }
+});
+
+function fakeManager(): DownloadManager {
+  const snapshot = {
+    stats: {},
+    session: { packages: {}, items: {}, packageOrder: [] },
+    speedText: "",
+    etaText: "",
+    canStart: false,
+    canStop: false,
+    canPause: false
+  };
+  return {
+    getSnapshot: () => snapshot,
+    getPackageLogPath: () => null,
+    getItemLogPath: () => null
+  } as unknown as DownloadManager;
+}
+
+describe("buildSupportBundle (async, non-blocking)", () => {
+  it("returns a Promise and produces a valid zip with overview + a real on-disk file", async () => {
+    const root = fs.mkdtempSync(path.join(os.tmpdir(), "rd-bundle-"));
+    tempDirs.push(root);
+    fs.writeFileSync(path.join(root, "debug_host.txt"), "host-info-test", "utf8");
+
+    const promise = buildSupportBundle(fakeManager(), root, { hostDiagnosticsMode: "none" });
+    expect(promise).toBeInstanceOf(Promise);
+
+    const buffer = await promise;
+    expect(Buffer.isBuffer(buffer)).toBe(true);
+    expect(buffer.length).toBeGreaterThan(0);
+
+    const entries = new AdmZip(buffer).getEntries().map((e) => e.entryName);
+    expect(entries).toContain("overview/meta.json");
+    expect(entries).toContain("overview/settings.json");
+    expect(entries).toContain("runtime/debug_host.txt");
+
+    const hostEntry = new AdmZip(buffer).getEntry("runtime/debug_host.txt");
+    expect(hostEntry?.getData().toString("utf8")).toBe("host-info-test");
+  });
+
+  it("does not block the event loop while building (a concurrent timer still fires)", async () => {
+    const root = fs.mkdtempSync(path.join(os.tmpdir(), "rd-bundle-"));
+    tempDirs.push(root);
+
+    let timerFired = false;
+    const timer = setTimeout(() => { timerFired = true; }, 0);
+    await buildSupportBundle(fakeManager(), root, { hostDiagnosticsMode: "none" });
+    clearTimeout(timer);
+    await new Promise((resolve) => setTimeout(resolve, 0));
+    expect(timerFired).toBe(true);
+  });
+});