feat(gateway): add node capability negotiation foundation

src/config/schema.ts

@@ -79,6 +79,15 @@ const serverDiscoverySchema = z.object({
   txt: z.record(z.string(), z.string()).default({}),
 }).default({});
 
+const serverNodePolicySchema = z.object({
+  /** Enable node registration/capability RPC surface. */
+  enabled: z.boolean().default(false),
+  /** Allowed node roles for node.register. */
+  allowed_roles: z.array(z.string().min(1)).default(['companion']),
+  /** Optional feature gates exposed via system/node capability APIs. */
+  feature_gates: z.record(z.string(), z.boolean()).default({}),
+}).default({});
+
 const serverSchema = z.object({
   tailscale: tailscaleSchema,
   localhost: z.boolean().default(true),
@@ -97,6 +106,8 @@ const serverSchema = z.object({
   ws_rate_limit: wsRateLimitSchema,
   /** Per-session gateway lane queue behavior. */
   queue: laneQueueSchema,
+  /** Optional companion-node registration/capability settings. */
+  nodes: serverNodePolicySchema,
   /** Optional Bonjour/mDNS advertisement settings. */
   discovery: serverDiscoverySchema,
 });