CUB-123: integrate gateway, wire PostgreSQL repositories, add SSE streaming

- Create repository/ package with pgx-backed CRUD for agents, sessions, tasks, projects
- Define AgentRepo/SessionRepo/TaskRepo/ProjectRepo interfaces
- Update handler to use repository interfaces instead of in-memory stores
- Add SSE broker with GET /api/events endpoint (text/event-stream)
- Add gateway client that polls OpenClaw for agent states
- Add GATEWAY_URL and GATEWAY_POLL_INTERVAL config fields
- Seed 5 demo agents (Otto, Rex, Dex, Hex, Pip) on empty DB
- Update router to wire SSE broker
- All 21 handler tests pass with mock repos

go-backend/internal/config/config.go

@@ -5,26 +5,31 @@ package config
 import (
 	"os"
 	"strconv"
+	"time"
 )
 
 // Config holds all application configuration.
 type Config struct {
-	Port         int
-	DatabaseURL  string
-	CORSOrigin   string
-	LogLevel     string
-	Environment  string
+	Port              int
+	DatabaseURL       string
+	CORSOrigin        string
+	LogLevel          string
+	Environment       string
+	GatewayURL        string
+	GatewayPollInterval time.Duration
 }
 
 // Load reads configuration from environment variables, applying defaults where
 // values are not set. All secrets come from the environment — nothing is hardcoded.
 func Load() *Config {
 	return &Config{
-		Port:        getEnvInt("PORT", 8080),
-		DatabaseURL: getEnv("DATABASE_URL", "postgres://controlcenter:controlcenter@localhost:5432/controlcenter?sslmode=disable"),
-		CORSOrigin:  getEnv("CORS_ORIGIN", "*"),
-		LogLevel:    getEnv("LOG_LEVEL", "info"),
-		Environment: getEnv("ENVIRONMENT", "development"),
+		Port:                getEnvInt("PORT", 8080),
+		DatabaseURL:         getEnv("DATABASE_URL", "postgres://controlcenter:controlcenter@localhost:5432/controlcenter?sslmode=disable"),
+		CORSOrigin:          getEnv("CORS_ORIGIN", "*"),
+		LogLevel:            getEnv("LOG_LEVEL", "info"),
+		Environment:         getEnv("ENVIRONMENT", "development"),
+		GatewayURL:          getEnv("GATEWAY_URL", "http://localhost:18789/api/agents"),
+		GatewayPollInterval: getEnvDuration("GATEWAY_POLL_INTERVAL", 5*time.Second),
 	}
 }
 
@@ -43,3 +48,12 @@ func getEnvInt(key string, fallback int) int {
 	}
 	return fallback
 }
+
+func getEnvDuration(key string, fallback time.Duration) time.Duration {
+	if v := os.Getenv(key); v != "" {
+		if d, err := time.ParseDuration(v); err == nil {
+			return d
+		}
+	}
+	return fallback
+}