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/main.py

@@ -55,7 +55,7 @@ async def lifespan(app: FastAPI):
     schedule_task.cancel()
 
 
-app = FastAPI(title="StackPilot", version="0.21.4", lifespan=lifespan)
+app = FastAPI(title="StackPilot", version="0.21.5", lifespan=lifespan)
 
 app.add_middleware(
     CORSMiddleware,