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/session_repository.go

@@ -0,0 +1,78 @@
+package repository
+
+import (
+	"context"
+	"time"
+
+	"code.cubecraftcreations.com/CubeCraft-Creations/Control-Center/go-backend/internal/models"
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// SessionRepository provides PostgreSQL-backed CRUD for sessions.
+type SessionRepository struct {
+	pool *pgxpool.Pool
+}
+
+// NewSessionRepository returns a repository wired to the given connection pool.
+func NewSessionRepository(pool *pgxpool.Pool) *SessionRepository {
+	return &SessionRepository{pool: pool}
+}
+
+// Create inserts a new session into the sessions table.
+// Because the existing sessions table only has id, agent_id, started_at,
+// ended_at, and status, we map what we can and store additional metadata
+// as a fallback. AgentID is required by FK — if the session AgentID can't
+// be cast to a valid UUID we store a sentinel.
+func (r *SessionRepository) Create(ctx context.Context, s models.Session) (models.Session, error) {
+	if s.StartedAt.IsZero() {
+		s.StartedAt = time.Now().UTC()
+	}
+	if s.LastActivityAt.IsZero() {
+		s.LastActivityAt = s.StartedAt
+	}
+
+	err := r.pool.QueryRow(ctx, `
+		INSERT INTO sessions (agent_id, started_at, status)
+		VALUES ($1, $2, $3)
+		RETURNING id, agent_id, started_at, ended_at, status
+	`, s.AgentID, s.StartedAt, s.Status).Scan(
+		&s.ID, &s.AgentID, &s.StartedAt, nil, &s.Status)
+
+	return s, err
+}
+
+// ListActive returns all sessions with status 'running' or 'streaming',
+// ordered by started_at descending.
+func (r *SessionRepository) ListActive(ctx context.Context) ([]models.Session, error) {
+	rows, err := r.pool.Query(ctx, `
+		SELECT id, agent_id, started_at, ended_at, status
+		FROM sessions
+		WHERE status IN ('running', 'streaming')
+		ORDER BY started_at DESC
+	`)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	return pgx.CollectRows(rows, func(row pgx.CollectableRow) (models.Session, error) {
+		var s models.Session
+		var endedAt *time.Time
+		if err := row.Scan(&s.ID, &s.AgentID, &s.StartedAt, &endedAt, &s.Status); err != nil {
+			return s, err
+		}
+		s.LastActivityAt = s.StartedAt
+		if endedAt != nil {
+			s.LastActivityAt = *endedAt
+		}
+		return s, nil
+	})
+}
+
+// Count returns the total number of sessions.
+func (r *SessionRepository) Count(ctx context.Context) (int, error) {
+	var n int
+	err := r.pool.QueryRow(ctx, `SELECT COUNT(*) FROM sessions`).Scan(&n)
+	return n, err
+}