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/upload/channel.ts

@@ -94,10 +94,10 @@ async function sendAndWaitForUpload(
     let lastLoggedPercent = 0;
     let tempMsgId: number | null = null;
 
-    // Timeout: 10 minutes per GB, minimum 10 minutes
+    // Timeout: 15 minutes per GB, minimum 10 minutes
     const timeoutMs = Math.max(
       10 * 60_000,
-      (fileSizeMB / 1024) * 10 * 60_000
+      (fileSizeMB / 1024) * 15 * 60_000
     );
 
     const timer = setTimeout(() => {