feat: add remote worker system for distributed translation

- Add remote translator worker (Docker) that connects via WebSocket
- Add backend Go handlers for remote worker CRUD (REST + WebSocket)
- Add frontend Admin panel for managing remote workers
- Add ProtectedRoute component to secure admin routes
- Add PostgreSQL schema for remote_workers table
- Fix duplicate Load function in config.go
- Fix frontend duplicate fetchStatus function
- Fix Dockerfiles missing go.sum (use go mod download + tidy)

Features:
- Workers connect to server via WebSocket (no ports needed)
- API key authentication per worker
- Job assigner automatically distributes translation jobs
- Worker status tracking (online/offline/disabled)
- Timeout handling for stuck jobs

backend/Dockerfile

@@ -4,10 +4,11 @@ WORKDIR /app
 
 RUN apt-get update && apt-get install -y gcc musl-dev git
 
-COPY go.mod go.sum ./
+COPY go.mod ./
 RUN go mod download
 
 COPY . .
+RUN go mod tidy
 
 RUN CGO_ENABLED=0 GOOS=linux go build -buildvcs=false -o /server ./cmd/server