fix: improve worker error handling and reliability

1. Distinguish failure reasons: inspect error messages to label skipped
   packages as DOWNLOAD_FAILED, UPLOAD_FAILED, or EXTRACT_FAILED
   instead of catch-all DOWNLOAD_FAILED.

2. Detect orphaned uploads: before uploading, check if the same content
   hash already has a successful upload on the destination channel. Reuse
   the existing message ID instead of re-uploading (prevents duplicates
   when worker crashed between upload and DB write).

3. Increase timeouts: download from max(5min, GB*10min) to
   max(10min, GB*15min), upload from GB*10min to GB*15min.
   Prevents premature timeouts on slow connections.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

worker/src/tdlib/download.ts

@@ -354,10 +354,10 @@ export async function downloadFile(
     let lastLoggedPercent = 0;
     let settled = false;
 
-    // Timeout: 10 minutes per GB, minimum 5 minutes
+    // Timeout: 15 minutes per GB, minimum 10 minutes
     const timeoutMs = Math.max(
-      5 * 60_000,
-      (totalBytes / (1024 * 1024 * 1024)) * 10 * 60_000
+      10 * 60_000,
+      (totalBytes / (1024 * 1024 * 1024)) * 15 * 60_000
     );
     const timer = setTimeout(() => {
       if (!settled) {