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

init-db/35-remote-workers.sql

@@ -0,0 +1,31 @@
+-- Tabla de workers remotos
+CREATE TABLE IF NOT EXISTS remote_workers (
+    id SERIAL PRIMARY KEY,
+    name VARCHAR(255) NOT NULL,
+    api_key VARCHAR(64) UNIQUE NOT NULL,
+    capabilities VARCHAR(50) DEFAULT 'cpu',
+    status VARCHAR(20) DEFAULT 'offline',
+    last_seen TIMESTAMP,
+    created_at TIMESTAMP DEFAULT NOW()
+);
+
+-- Añadir columnas a traducciones para workers remotos
+ALTER TABLE traducciones ADD COLUMN IF NOT EXISTS worker_id INTEGER REFERENCES remote_workers(id);
+ALTER TABLE traducciones ADD COLUMN IF NOT EXISTS assigned_at TIMESTAMP;
+
+-- Índices para workers remotos
+CREATE INDEX IF NOT EXISTS idx_remote_workers_status ON remote_workers(status);
+CREATE INDEX IF NOT EXISTS idx_remote_workers_api_key ON remote_workers(api_key);
+
+-- Índice para buscar jobs disponibles por capabilities
+CREATE INDEX IF NOT EXISTS idx_traducciones_pending_worker 
+    ON traducciones(lang_to, status, worker_id) 
+    WHERE status = 'pending' AND worker_id IS NULL;
+
+-- Índice para jobs asignados (para cleanup de timeout)
+CREATE INDEX IF NOT EXISTS idx_traducciones_assigned_timeout 
+    ON traducciones(assigned_at) 
+    WHERE status = 'assigned' AND assigned_at IS NOT NULL;
+
+-- Tabla de workers remotos conectados (en memoria = no persistir, pero referenciar)
+-- El status se actualiza desde el WebSocket handler