feat(license): distributed license enforcement across multi-node setups (#359)

* feat(license): distributed license enforcement across multi-node setups

The primary instance's license tier is now asserted to remote nodes on
every proxied HTTP and WebSocket request via trusted headers. Remote
nodes honor the assertion only when the request carries a valid
node_proxy JWT, preventing unauthorized elevation from browsers or API
tokens. Falls back to local license tier for direct access.

* fix(test): remove unused vi import in distributed-license tests

docs/features/licensing.mdx

@@ -55,6 +55,12 @@ Active licenses are re-validated every **72 hours** against the Lemon Squeezy AP
 
 To manage your subscription (update payment method, view invoices, cancel, or switch plans), visit the [Lemon Squeezy customer portal](https://app.lemonsqueezy.com/my-orders) or use the link in your purchase confirmation email.
 
+## Multi-node license enforcement
+
+If you manage multiple servers through Sencho's [multi-node feature](/features/multi-node), you only need a license on your **primary instance**. All remote nodes automatically inherit the primary's license tier for proxied requests — no per-node activation required.
+
+For details on how this works, see [License enforcement across nodes](/features/multi-node#license-enforcement-across-nodes).
+
 ## Deactivating a license
 
 To transfer your license to a different instance: