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/repository/interfaces.go

@@ -0,0 +1,38 @@
+package repository
+
+import (
+	"context"
+
+	"code.cubecraftcreations.com/CubeCraft-Creations/Control-Center/go-backend/internal/models"
+)
+
+// AgentRepo is the interface for agent persistence operations.
+type AgentRepo interface {
+	Create(ctx context.Context, a models.AgentCardData) error
+	Get(ctx context.Context, id string) (models.AgentCardData, error)
+	List(ctx context.Context, statusFilter models.AgentStatus) ([]models.AgentCardData, error)
+	Update(ctx context.Context, id string, req models.UpdateAgentRequest) (models.AgentCardData, error)
+	Delete(ctx context.Context, id string) error
+	Count(ctx context.Context) (int, error)
+}
+
+// SessionRepo is the interface for session persistence operations.
+type SessionRepo interface {
+	Create(ctx context.Context, s models.Session) (models.Session, error)
+	ListActive(ctx context.Context) ([]models.Session, error)
+	Count(ctx context.Context) (int, error)
+}
+
+// TaskRepo is the interface for task persistence operations.
+type TaskRepo interface {
+	Create(ctx context.Context, t models.Task) (models.Task, error)
+	ListRecent(ctx context.Context) ([]models.Task, error)
+	Count(ctx context.Context) (int, error)
+}
+
+// ProjectRepo is the interface for project persistence operations.
+type ProjectRepo interface {
+	Create(ctx context.Context, p models.Project) (models.Project, error)
+	List(ctx context.Context) ([]models.Project, error)
+	Count(ctx context.Context) (int, error)
+}