fix(repo,service): SCALE-002 — push pagination into SQL for target/issuer/team/agent_group

Sprint 2 unified-master-audit closure. Pre-fix four service List
endpoints (target, issuer, team, agent_group) called repoFoo.List(ctx)
to fetch the full table then sliced in memory:

    rows, _ := s.repo.List(ctx)
    total := int64(len(rows))
    start := (page - 1) * perPage
    end := start + perPage
    return rows[start:end], total, nil

This page-sliced in memory pattern marshals every row per request —
fine on small fleets but unacceptable for multi-tenant or large-fleet
deploys. The agent_group case was worse — the service explicitly
ignored page/perPage and returned the entire slice.

Fix:
  - New ListPaginated(ctx, limit, offset) method on each of the four
    repositories. Postgres implementations push LIMIT + OFFSET into
    the SQL plus a SELECT COUNT(*) for the total. Mirrors the cursor
    pattern already in internal/repository/postgres/certificate.go.
  - Each ListPaginated normalises limit≤0→50 and offset<0→0,
    matching the service-layer defaults that already existed.
  - Repository interfaces grow the new method so adapters stay
    swappable.
  - Service List methods now call repoFoo.ListPaginated(ctx, perPage,
    (page-1)*perPage) directly — no more memory-slice.
  - AgentGroupService.ListAgentGroups closes the Bundle E / Audit
    L-020 'page/perPage unused' gap.

Test changes:
  - sliceWindow generic helper in testutil_test.go mirrors the SQL
    LIMIT/OFFSET semantics for in-memory mocks.
  - Six mock implementers (lifecycle_test, testutil_test x2,
    agent_group_test, team_test) gain ListPaginated methods.
  - TestTeamService_List_SCALE002_PaginationPropagatesToRepo pins
    the page=2, perPage=3 → 3 rows of 10 invariant.

Closes SCALE-002.

internal/repository/postgres/target.go

@@ -82,6 +82,48 @@ func (r *TargetRepository) List(ctx context.Context) ([]*domain.DeploymentTarget
 	return targets, nil
 }
 
+// ListPaginated returns a slice of deployment targets bounded by limit/offset
+// plus the total row count. SCALE-002 closure (Sprint 2, 2026-05-16) — pushes
+// pagination into SQL so the admin UI doesn't marshal the entire targets
+// table per request. limit≤0 is normalised to 50; offset<0 to 0.
+func (r *TargetRepository) ListPaginated(ctx context.Context, limit, offset int) ([]*domain.DeploymentTarget, int64, error) {
+	if limit <= 0 {
+		limit = 50
+	}
+	if offset < 0 {
+		offset = 0
+	}
+
+	var total int64
+	if err := r.db.QueryRowContext(ctx, `SELECT COUNT(*) FROM deployment_targets`).Scan(&total); err != nil {
+		return nil, 0, fmt.Errorf("failed to count targets: %w", err)
+	}
+
+	rows, err := r.db.QueryContext(ctx, `
+		SELECT `+targetSelectColumns+`
+		FROM deployment_targets
+		ORDER BY created_at DESC
+		LIMIT $1 OFFSET $2
+	`, limit, offset)
+	if err != nil {
+		return nil, 0, fmt.Errorf("failed to query targets: %w", err)
+	}
+	defer rows.Close()
+
+	var targets []*domain.DeploymentTarget
+	for rows.Next() {
+		var t domain.DeploymentTarget
+		if err := scanTarget(rows, &t); err != nil {
+			return nil, 0, fmt.Errorf("failed to scan target: %w", err)
+		}
+		targets = append(targets, &t)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, 0, fmt.Errorf("error iterating target rows: %w", err)
+	}
+	return targets, total, nil
+}
+
 // Get retrieves a target by ID
 func (r *TargetRepository) Get(ctx context.Context, id string) (*domain.DeploymentTarget, error) {
 	var target domain.DeploymentTarget