fix: add download progress/completion logging to frontend

Uploads already logged start, every-1-GiB progress, and completion.
Downloads only logged start — now also log:
- Completion with file size (Download complete: file.7z (1.9 GiB))
- Failure with wget exit code
- Periodic progress every ~1 GiB with speed and ETA

frontend/app.py

@@ -222,6 +222,7 @@ async def session_upload(
         "vm_name": vm_name,
         "start_time": time.time(),
         "content_length": content_length,
+        "_last_logged_bytes": 0,
     }
 
     return JSONResponse({
@@ -261,6 +262,7 @@ async def session_progress(filename: str):
         # Process exited
         _active_downloads.pop(filename, None)
         if poll != 0:
+            logger.error("Download failed: %s (wget exited with code %d)", filename, poll)
             if dest.exists():
                 dest.unlink(missing_ok=True)
             return JSONResponse({
@@ -270,6 +272,7 @@ async def session_progress(filename: str):
             })
         # Success
         final_bytes = dest.stat().st_size
+        logger.info("Download complete: %s (%.1f GiB)", filename, final_bytes / (1024**3))
         return JSONResponse({
             "phase": "complete",
             "file_size_bytes": final_bytes,
@@ -320,6 +323,14 @@ async def session_progress(filename: str):
         # Already handled above; this line is unreachable but kept for clarity
         pass
 
+    # Log progress periodically (every ~1 GiB)
+    last_logged = info.get("_last_logged_bytes", 0)
+    if current_bytes - last_logged >= 1024**3:
+        info["_last_logged_bytes"] = current_bytes
+        logger.info("Downloading: %s — %.1f GiB (%.1f MB/s)%s",
+                    filename, current_bytes / (1024**3), speed_mbps,
+                    f" ETA {eta_str}" if eta_str else "")
+
     return JSONResponse({
         "phase": "downloading",
         "file_size_bytes": current_bytes,