docs: add documentation for 8 new Vapi voices

Add documentation entries for Leo, Zoe, Mia, Jess, Zac, Dan, Leah, and
Tara voices to the Vapi Voices documentation page.

These are Orpheus-based voices that have been added to Vapi's self-hosted
voice offering. Documentation follows the same format as existing Elliot
and Savannah entries.

Note: Audio sample files need to be added separately to complete the
audio preview functionality.

Linear Issue: VAP-11667

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Vapi Tasker

fern/providers/voice/vapi-voices.mdx

@@ -37,6 +37,62 @@ These voices are fully supported and recommended for new assistants.
 - **Characteristics**: Southern American accent
 - **Sample Audio**: <audio controls src="/static/audio/savannah-sample.wav">Your browser does not support the audio element.</audio>
 
+### Leo
+- **Gender**: Male
+- **Accent**: American
+- **Age**: Young Adult
+- **Characteristics**: Natural, conversational
+- **Sample Audio**: <audio controls src="/static/audio/leo-sample.wav">Your browser does not support the audio element.</audio>
+
+### Zoe
+- **Gender**: Female
+- **Accent**: American
+- **Age**: Young Adult
+- **Characteristics**: Natural, conversational
+- **Sample Audio**: <audio controls src="/static/audio/zoe-sample.wav">Your browser does not support the audio element.</audio>
+
+### Mia
+- **Gender**: Female
+- **Accent**: American
+- **Age**: Young Adult
+- **Characteristics**: Natural, conversational
+- **Sample Audio**: <audio controls src="/static/audio/mia-sample.wav">Your browser does not support the audio element.</audio>
+
+### Jess
+- **Gender**: Female
+- **Accent**: American
+- **Age**: Young Adult
+- **Characteristics**: Natural, conversational
+- **Sample Audio**: <audio controls src="/static/audio/jess-sample.wav">Your browser does not support the audio element.</audio>
+
+### Zac
+- **Gender**: Male
+- **Accent**: American
+- **Age**: Young Adult
+- **Characteristics**: Natural, conversational
+- **Sample Audio**: <audio controls src="/static/audio/zac-sample.wav">Your browser does not support the audio element.</audio>
+
+### Dan
+- **Gender**: Male
+- **Accent**: American
+- **Age**: Young Adult
+- **Characteristics**: Natural, conversational
+- **Sample Audio**: <audio controls src="/static/audio/dan-sample.wav">Your browser does not support the audio element.</audio>
+
+### Leah
+- **Gender**: Female
+- **Accent**: American
+- **Age**: Young Adult
+- **Characteristics**: Natural, conversational
+- **Sample Audio**: <audio controls src="/static/audio/leah-sample.wav">Your browser does not support the audio element.</audio>
+
+### Tara
+- **Gender**: Female
+- **Accent**: American
+- **Age**: Young Adult
+- **Characteristics**: Natural, conversational
+- **Sample Audio**: <audio controls src="/static/audio/tara-sample.wav">Your browser does not support the audio element.</audio>
+
 ## How to Use
 
 1. Select a voice from our Active Voices collection