File browser: upload progress bar (0.21.5)

filesApi.upload now accepts an onProgress callback wired to axios
onUploadProgress; the Files page shows a progress bar with percentage
while uploading. Single-file upload tracks that file's bytes; folder
upload tracks overall progress across the N files (file i/N + current
file's bytes).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/agent_app.py

@@ -62,7 +62,7 @@ def _map_docker(exc: DockerError):
         raise HTTPException(status_code=code, detail=exc.detail or exc.error)
     raise exc  # falls through to the global 502 DockerError handler
 
-AGENT_VERSION = "0.21.4"
+AGENT_VERSION = "0.21.5"
 
 
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