Async FS optimizations, exponential backoff, cleanup dedup and release v1.4.72

- Convert all sync FS ops (existsSync, readdirSync, statSync, writeFileSync,
  rmSync, renameSync) to async equivalents across download-manager, extractor,
  cleanup, storage, and logger to prevent UI freezes
- Replace linear retry delays with exponential backoff + jitter to prevent
  retry storms with many parallel downloads
- Deduplicate resolveArchiveItems into single shared function
- Replace Array.shift() O(N) in bandwidth chart with slice-based trimming
- Make logger rotation async in the async flush path

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main/storage.ts

@@ -477,9 +477,7 @@ let asyncSaveQueued: { paths: StoragePaths; payload: string } | null = null;
 
 async function writeSessionPayload(paths: StoragePaths, payload: string): Promise<void> {
   await fs.promises.mkdir(paths.baseDir, { recursive: true });
-  if (fs.existsSync(paths.sessionFile)) {
-    await fsp.copyFile(paths.sessionFile, sessionBackupPath(paths.sessionFile)).catch(() => {});
-  }
+  await fsp.copyFile(paths.sessionFile, sessionBackupPath(paths.sessionFile)).catch(() => {});
   const tempPath = sessionTempPath(paths.sessionFile, "async");
   await fsp.writeFile(tempPath, payload, "utf8");
   try {