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/integration/lifecycle_test.go

@@ -961,6 +961,25 @@ func (m *mockTargetRepository) List(ctx context.Context) ([]*domain.DeploymentTa
 	return targets, nil
 }
 
+// ListPaginated mirrors the SQL-side window. SCALE-002 closure (Sprint 2).
+func (m *mockTargetRepository) ListPaginated(ctx context.Context, limit, offset int) ([]*domain.DeploymentTarget, int64, error) {
+	all, _ := m.List(ctx)
+	if offset < 0 {
+		offset = 0
+	}
+	if offset >= len(all) {
+		return nil, int64(len(all)), nil
+	}
+	if limit <= 0 {
+		return all[offset:], int64(len(all)), nil
+	}
+	end := offset + limit
+	if end > len(all) {
+		end = len(all)
+	}
+	return all[offset:end], int64(len(all)), nil
+}
+
 func (m *mockTargetRepository) Get(ctx context.Context, id string) (*domain.DeploymentTarget, error) {
 	target, ok := m.targets[id]
 	if !ok {
@@ -1233,6 +1252,25 @@ func (m *mockIssuerRepository) List(ctx context.Context) ([]*domain.Issuer, erro
 	return issuers, nil
 }
 
+// ListPaginated mirrors the SQL-side window. SCALE-002 closure (Sprint 2).
+func (m *mockIssuerRepository) ListPaginated(ctx context.Context, limit, offset int) ([]*domain.Issuer, int64, error) {
+	all, _ := m.List(ctx)
+	if offset < 0 {
+		offset = 0
+	}
+	if offset >= len(all) {
+		return nil, int64(len(all)), nil
+	}
+	if limit <= 0 {
+		return all[offset:], int64(len(all)), nil
+	}
+	end := offset + limit
+	if end > len(all) {
+		end = len(all)
+	}
+	return all[offset:end], int64(len(all)), nil
+}
+
 func (m *mockIssuerRepository) Get(ctx context.Context, id string) (*domain.Issuer, error) {
 	issuer, ok := m.issuers[id]
 	if !ok {