[e2e] Add management-side agent-network scenarios (Pillar 2)

Port the API-driven agent-network scenarios from the bash suites to Go,
sharing one combined server per package run (TestMain) with each test
owning its resource cleanup. Drives the /api/agent-network/* endpoints
through the shared REST client's NewRequest primitive with the generated
api types.

Scenarios:
- provider lifecycle (create/get/list/delete + 404 after delete)
- provider validation (missing api_key, unknown catalog id → 4xx)
- settings collection-toggle round-trip with cluster/subdomain immutability
- policy window floor (reject <60s enabled limit, accept at 60s)
- consumption read endpoint returns an array

All deterministic and dependency-free (dummy provider keys; no upstream
calls), so they run headless in CI.

e2e/harness/agentnetwork.go

@@ -0,0 +1,101 @@
+//go:build e2e
+
+package harness
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+
+	"github.com/netbirdio/netbird/shared/management/http/api"
+)
+
+// The shared REST client doesn't (yet) expose typed agent-network methods, so
+// these helpers drive the /api/agent-network/* endpoints through the client's
+// NewRequest primitive — reusing its auth, error handling (rest.APIError on
+// non-2xx), and transport — while still speaking the generated api types.
+
+// anRequest issues an agent-network API call and decodes the JSON response into
+// T. A non-2xx response surfaces as a *rest.APIError from the client, which
+// tests inspect for negative-path status assertions.
+func anRequest[T any](ctx context.Context, c *Combined, method, path string, body any) (T, error) {
+	var out T
+	var reader io.Reader
+	if body != nil {
+		bs, err := json.Marshal(body)
+		if err != nil {
+			return out, fmt.Errorf("marshal %s %s: %w", method, path, err)
+		}
+		reader = bytes.NewReader(bs)
+	}
+
+	resp, err := c.api.NewRequest(ctx, method, path, reader, nil)
+	if err != nil {
+		return out, err
+	}
+	defer resp.Body.Close()
+
+	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
+		return out, fmt.Errorf("decode %s %s response: %w", method, path, err)
+	}
+	return out, nil
+}
+
+// anDelete issues a DELETE and discards the (empty-object) body.
+func anDelete(ctx context.Context, c *Combined, path string) error {
+	resp, err := c.api.NewRequest(ctx, http.MethodDelete, path, nil, nil)
+	if err != nil {
+		return err
+	}
+	resp.Body.Close()
+	return nil
+}
+
+// CreateProvider creates an agent-network provider.
+func (c *Combined) CreateProvider(ctx context.Context, req api.AgentNetworkProviderRequest) (api.AgentNetworkProvider, error) {
+	return anRequest[api.AgentNetworkProvider](ctx, c, http.MethodPost, "/api/agent-network/providers", req)
+}
+
+// GetProvider fetches a provider by id.
+func (c *Combined) GetProvider(ctx context.Context, id string) (api.AgentNetworkProvider, error) {
+	return anRequest[api.AgentNetworkProvider](ctx, c, http.MethodGet, "/api/agent-network/providers/"+id, nil)
+}
+
+// ListProviders returns all providers for the account.
+func (c *Combined) ListProviders(ctx context.Context) ([]api.AgentNetworkProvider, error) {
+	return anRequest[[]api.AgentNetworkProvider](ctx, c, http.MethodGet, "/api/agent-network/providers", nil)
+}
+
+// DeleteProvider removes a provider by id.
+func (c *Combined) DeleteProvider(ctx context.Context, id string) error {
+	return anDelete(ctx, c, "/api/agent-network/providers/"+id)
+}
+
+// CreatePolicy creates an agent-network policy.
+func (c *Combined) CreatePolicy(ctx context.Context, req api.AgentNetworkPolicyRequest) (api.AgentNetworkPolicy, error) {
+	return anRequest[api.AgentNetworkPolicy](ctx, c, http.MethodPost, "/api/agent-network/policies", req)
+}
+
+// DeletePolicy removes a policy by id.
+func (c *Combined) DeletePolicy(ctx context.Context, id string) error {
+	return anDelete(ctx, c, "/api/agent-network/policies/"+id)
+}
+
+// GetSettings returns the account's agent-network settings row. It exists only
+// after the first provider create bootstraps it.
+func (c *Combined) GetSettings(ctx context.Context) (api.AgentNetworkSettings, error) {
+	return anRequest[api.AgentNetworkSettings](ctx, c, http.MethodGet, "/api/agent-network/settings", nil)
+}
+
+// UpdateSettings applies the mutable collection toggles.
+func (c *Combined) UpdateSettings(ctx context.Context, req api.AgentNetworkSettingsRequest) (api.AgentNetworkSettings, error) {
+	return anRequest[api.AgentNetworkSettings](ctx, c, http.MethodPut, "/api/agent-network/settings", req)
+}
+
+// ListConsumption returns the account's consumption rows (possibly empty).
+func (c *Combined) ListConsumption(ctx context.Context) ([]api.AgentNetworkConsumption, error) {
+	return anRequest[[]api.AgentNetworkConsumption](ctx, c, http.MethodGet, "/api/agent-network/consumption", nil)
+}