[management] Add dashboard_features account setting for per-section visibility

Introduce a nullable dashboard_features object on account settings, serialized
to a single JSON column so new dashboard sections can be added without schema
changes. Starts with agent_network (show the Agent Network menu for an account
without the deployment flag). Wires the API handler mapping, the pgx GetAccount
loader, and adds store round-trip and handler tests.

shared/management/http/api/openapi.yml

@@ -379,6 +379,8 @@ components:
           description: Limits the dashboard to the Agent Network surface for this account. Set for accounts created via netbird.ai signups and can be disabled later.
           type: boolean
           example: false
+        dashboard_features:
+          $ref: '#/components/schemas/AccountDashboardFeatures'
         embedded_idp_enabled:
           description: Indicates whether the embedded identity provider (Dex) is enabled for this account. This is a read-only field.
           type: boolean
@@ -407,6 +409,14 @@ components:
         - regular_users_view_blocked
         - peer_expose_enabled
         - peer_expose_groups
+    AccountDashboardFeatures:
+      description: Per-account dashboard section visibility overrides. Omitted keys follow the default dashboard behavior.
+      type: object
+      properties:
+        agent_network:
+          description: When true, the Agent Network menu is shown for the account even without the deployment feature flag.
+          type: boolean
+          example: true
     AccountExtraSettings:
       type: object
       properties:

shared/management/http/api/types.gen.go

@@ -1612,6 +1612,12 @@ type Account struct {
 	Settings   AccountSettings   `json:"settings"`
 }
 
+// AccountDashboardFeatures Per-account dashboard section visibility overrides. Omitted keys follow the default dashboard behavior.
+type AccountDashboardFeatures struct {
+	// AgentNetwork When true, the Agent Network menu is shown for the account even without the deployment feature flag.
+	AgentNetwork *bool `json:"agent_network,omitempty"`
+}
+
 // AccountExtraSettings defines model for AccountExtraSettings.
 type AccountExtraSettings struct {
 	// NetworkTrafficLogsEnabled Enables or disables network traffic logging. If enabled, all network traffic events from peers will be stored.
@@ -1656,6 +1662,9 @@ type AccountSettings struct {
 	// AutoUpdateVersion Set Clients auto-update version. "latest", "disabled", or a specific version (e.g "0.50.1")
 	AutoUpdateVersion *string `json:"auto_update_version,omitempty"`
 
+	// DashboardFeatures Per-account dashboard section visibility overrides. Omitted keys follow the default dashboard behavior.
+	DashboardFeatures *AccountDashboardFeatures `json:"dashboard_features,omitempty"`
+
 	// DnsDomain Allows to define a custom dns domain for the account
 	DnsDomain *string `json:"dns_domain,omitempty"`