[management,proxy] Add agentgateway integration (#7274)

* [management] Add agentgateway provider catalog entry

Allow Agent Network providers to target an operator-supplied agentgateway proxy while stamping trusted NetBird identity headers.

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

* [proxy] Allow trusted Agent Network identity headers

Permit only the built-in identity injector to replace the two reserved agentgateway attribution headers while keeping them blocked for every other middleware.

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

* [management,proxy] Add multi-vendor gateway routing

Let one Agent Network route declare multiple parser surfaces while preserving the existing singular vendor wire field.

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

* [management] Update router test for model policies

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

* [proxy] Cover reserved header policy

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

* [management] Add agentgateway model discovery

Use agentgateway's OpenAI-compatible models endpoint and omit wildcard patterns until NetBird can authorize and price them consistently.

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

---------

Signed-off-by: Daneyon Hansen <daneyon.hansen@solo.io>

management/internals/modules/agentnetwork/synthesizer_test.go

@@ -6,9 +6,9 @@ import (
 	"testing"
 	"time"
 
-	"go.uber.org/mock/gomock"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"go.uber.org/mock/gomock"
 
 	"github.com/netbirdio/netbird/management/internals/modules/agentnetwork/catalog"
 	"github.com/netbirdio/netbird/management/internals/modules/agentnetwork/types"
@@ -497,6 +497,55 @@ func TestSynthesizeServices_IdentityInject_LiteLLM(t *testing.T) {
 	assert.Equal(t, "x-litellm-tags", entry.HeaderPair.TagsHeader)
 }
 
+func TestBuildIdentityInjectConfigJSON_Agentgateway(t *testing.T) {
+	provider := &types.Provider{
+		ID:         "prov-agentgateway",
+		ProviderID: "agentgateway",
+	}
+
+	raw, err := buildIdentityInjectConfigJSON(
+		[]*types.Provider{provider},
+		map[string][]string{provider.ID: []string{"grp-eng"}},
+	)
+	require.NoError(t, err)
+
+	var cfg identityInjectConfig
+	require.NoError(t, json.Unmarshal(raw, &cfg))
+	require.Len(t, cfg.Providers, 1)
+
+	rule := cfg.Providers[0]
+	assert.Equal(t, provider.ID, rule.ProviderID)
+	require.NotNil(t, rule.HeaderPair)
+	assert.Nil(t, rule.JSONMetadata)
+	assert.Equal(t, "x-netbird-user-id", rule.HeaderPair.EndUserIDHeader)
+	assert.Equal(t, "x-netbird-groups", rule.HeaderPair.TagsHeader)
+	assert.False(t, rule.HeaderPair.EndUserIDInBody)
+	assert.False(t, rule.HeaderPair.TagsInBody)
+}
+
+func TestBuildRouterConfigJSON_AgentgatewayVendors(t *testing.T) {
+	provider := &types.Provider{
+		ID:          "prov-agentgateway",
+		ProviderID:  "agentgateway",
+		UpstreamURL: "https://gateway.example.com",
+		APIKey:      "virtual-key",
+	}
+
+	raw, err := buildRouterConfigJSON(
+		[]*types.Provider{provider},
+		map[string][]string{provider.ID: {"grp-eng"}},
+		nil,
+	)
+	require.NoError(t, err)
+
+	var cfg routerConfig
+	require.NoError(t, json.Unmarshal(raw, &cfg))
+	require.Len(t, cfg.Providers, 1)
+	assert.Empty(t, cfg.Providers[0].Vendor,
+		"the singular vendor remains empty for a multi-surface gateway")
+	assert.Equal(t, []string{"openai", "anthropic"}, cfg.Providers[0].Vendors)
+}
+
 // TestSynthesizeServices_IdentityInject_Bifrost_OperatorOverrides
 // covers the customizable HeaderPair contract. The Bifrost catalog
 // entry sets HeaderPair.Customizable=true with x-bf-dim-* defaults