fix: replace playht voice examples with 11labs (#631)

Author: goosewin

fern/calls/customer-join-timeout.mdx

@@ -140,7 +140,7 @@ Configure `customerJoinTimeoutSeconds` through the Vapi API for both permanent a
     call = client.calls.create_web(
       assistant={
         "model": {"provider": "openai", "model": "gpt-4.1-mini"},
-        "voice": {"provider": "playht", "voiceId": "jennifer"},
+        "voice": {"provider": "11labs", "voiceId": "cgSgspJ2msm6clMCkdW9"},
         "customer_join_timeout_seconds": 60
       }
     )
@@ -152,7 +152,7 @@ Configure `customerJoinTimeoutSeconds` through the Vapi API for both permanent a
          -d '{
            "assistant": {
              "model": {"provider": "openai", "model": "gpt-4.1-mini"},
-             "voice": {"provider": "playht", "voiceId": "jennifer"},
+             "voice": {"provider": "11labs", "voiceId": "cgSgspJ2msm6clMCkdW9"},
              "customerJoinTimeoutSeconds": 60
            }
          }'

fern/quickstart/phone.mdx

@@ -125,8 +125,8 @@ vapi assistant create
               },
               // Configure the voice
               voice: {
-                provider: 'playht',
-                voice_id: 'jennifer',
+                provider: '11labs',
+                voice_id: 'cgSgspJ2msm6clMCkdW9',
               },
               // Set the first message
               firstMessage: 'Hi there, this is Alex from TechSolutions customer support. How can I help you today?',
@@ -186,8 +186,8 @@ vapi assistant create
                     },
                     # Configure the voice
                     voice={
-                        "provider": "playht",
-                        "voice_id": "jennifer",
+                        "provider": "11labs",
+                        "voice_id": "cgSgspJ2msm6clMCkdW9",
                     },
                     # Set the first message
                     first_message="Hi there, this is Alex from TechSolutions customer support. How can I help you today?",
@@ -226,8 +226,8 @@ vapi assistant create
               ]
             },
             "voice": {
-              "provider": "playht",
-              "voice_id": "jennifer"
+              "provider": "11labs",
+              "voice_id": "cgSgspJ2msm6clMCkdW9"
             },
             "firstMessage": "Hi there, this is Alex from TechSolutions customer support. How can I help you today?"
           }'

fern/voice-fallback-plan.mdx

@@ -43,8 +43,8 @@ Add the `fallbackPlan` property to your assistant's voice configuration, and spe
                 "voiceId": "248be419-c632-4f23-adf1-5324ed7dbf1d"
             },
             {
-                "provider": "playht",
-                "voiceId": "jennifer"
+                "provider": "11labs",
+                "voiceId": "cgSgspJ2msm6clMCkdW9"
             }
         ]
     }