fix(gateway): harden channel health monitor recovery

src/config/zod-schema.ts

@@ -442,6 +442,7 @@ export const OpenClawSchema = z
           })
           .strict()
           .optional(),
+        channelHealthCheckMinutes: z.number().int().min(0).optional(),
         tailscale: z
           .object({
             mode: z.union([z.literal("off"), z.literal("serve"), z.literal("funnel")]).optional(),