Refactor API: Remove 'any' from EmbeddedChatApi and improve payload typing

Summary

packages/api/src/EmbeddedChatApi.ts currently relies on multiple explicit any types across callback signatures, stream payload handling, auth inputs, and message APIs. This reduces type safety and makes it easier to accidentally access unsafe or undefined fields, especially when working with dynamic DDP payloads.

Problem

• Explicit any appeared in:
  • message listeners
  • action/ui interaction listeners
  • autoLogin credentials
  • DDP stream callbacks (onStreamData)
  • sendMessage input
  • handleUiKitInteraction input
• Stream payloads were accessed without defensive narrowing (fields, eventName, args).
• SDK callback types are broad, so local guards are needed to keep runtime behavior while improving static safety.

Acceptance Criteria

• No explicit any remains in packages/api/src/EmbeddedChatApi.ts.
• connect() stream handling uses guarded/narrowed access.
• sendMessage and handleUiKitInteraction use typed inputs.
• packages/api builds successfully.
• No lint/type errors introduced.

Impact

• Better type safety and editor intelligence.
• Lower risk of runtime errors from malformed DDP payloads.
• No intended behavior changes at runtime.

Inizia da packages/api/src/EmbeddedChatApi.ts, leggendo connect(), le firme dei callback, autoLogin, sendMessage e handleUiKitInteraction. Esegui la build e i controlli di lint/tipi di packages/api sostituendo gli any espliciti con input tipizzati e accesso protetto allo stream; il lavoro è completato quando non rimane alcun any esplicito e il pacchetto viene compilato senza nuovi errori.