[agents] add pinnedDynamicVariables to conversation initiation

[anurag-umich]

Summary

• Adds pinnedDynamicVariables support across the SDK so callers can specify dynamic variable names that should not be overwritten by tool assignments during a conversation.
• This pairs with the backend change in elevenlabs/xi#29274 which accepts pinned_dynamic_variables on ConversationInitiationClientDataRequest and skips tool assignments for pinned variables.
• Once this SDK is released, the xi frontend can re-add lock toggles in the Dynamic Variables editor that pass pinned variables through startSession.

Changes

• packages/types: Added pinned_dynamic_variables to ConversationInitiationPayload in the asyncapi schema; regenerated TypeScript types
• packages/client: Added pinnedDynamicVariables?: string[] to BaseSessionConfig; mapped to pinned_dynamic_variables in constructOverrides
• packages/react-native: Added pinnedDynamicVariables to ConversationConfig, overrides.ts, ElevenLabsProvider, and useConversationSession hook

Test plan

• Verify type checks pass across all packages
• Start a conversation with pinnedDynamicVariables: ["var_name"] and verify pinned_dynamic_variables appears in the WebSocket init message
• Confirm pinned variables are not overwritten by tool assignments during the conversation

Made with Cursor

[kraenhansen]

We've been working on a re-architecture of the SDKs - if this is not time sensitive, could I ask you to rebase and target the next branch for this change instead? You would likely have to move a large part of the changes in the react-native package into the react package (as now our React Native SDK is just a thin wrapper around the React SDK).