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

Dockerfile.discovery

@@ -6,11 +6,15 @@ RUN apk add --no-cache git
 
 WORKDIR /app
 
-COPY backend/go.mod backend/go.sum ./
+COPY backend/go.mod ./
 RUN go mod download
 
 COPY backend/ ./
 
+RUN go mod tidy
+
+COPY backend/ ./
+
 RUN CGO_ENABLED=0 GOOS=linux go build -o /bin/discovery ./cmd/discovery
 
 FROM alpine:3.19