chore: Improve type safety in EmbeddedChatApi by removing any

[sudorishabh]

refactor(api): remove explicit any from EmbeddedChatApi with safer payload typing

This PR improves type safety in packages/api/src/EmbeddedChatApi.ts by removing explicit any usages and replacing them with concrete local types plus runtime narrowing where Rocket.Chat payloads are dynamic.

Acceptance Criteria fulfillment

• 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.

Fixes #1237

What Changed

• Added local type aliases/interfaces for:
  • message payloads (MessagePayload)
  • DDP stream payload envelope (DdpStreamMessage)
  • action and UI interaction payloads
  • auth input/token credential shapes for autoLogin
• Replaced explicit any in:
  • callback collections and listener method signatures
  • stream callbacks in connect()
  • sendMessage(...) argument type
  • handleUiKitInteraction(...) argument type
• Added payload normalization/narrowing helpers for:
  • fields.args handling
  • message ts normalization (including $date)
  • token credential shape normalization (service/access_token and serviceName/accessToken)
• Kept dynamic payload compatibility with index signatures ([key: string]: unknown) to avoid breaking external Rocket.Chat fields.

Why

• Prevent unsafe property access in stream and message callbacks.
• Improve TypeScript inference and editor autocomplete.
• Reduce runtime bug risk while preserving existing behavior.

Risk / Compatibility Notes

• Rocket.Chat SDK callback signatures are broad, so runtime guards are still required.
• Token credentials can arrive in multiple naming conventions; normalization handles both.

PR Test Details

• Verified no explicit any remains in EmbeddedChatApi.ts.
• Type/lint diagnostics for edited file are clean.
• yarn build in packages/api passes.

Note: The PR will be ready for live testing at https://rocketchat.github.io/EmbeddedChat/pulls/pr-1238 after approval.