fix(voice): keep clicked calls bound to their chat

[johnmatthewtennant]

Summary

Keeps Voice Conversation bound to the chat and window that initiated it without relying on transient focus.

• Authorizes starts against the foreground session generation and window ownership.
• Allows focus to move to voice controls without rejecting the clicked call.
• Rejects stale starts after a different window or session replaces the foreground target.

Reviewer example

Click the call control in a chat, then let focus move to the voice controls while startup is in flight. The call remains attached to that chat; a stale start from another foreground generation is rejected.

Testing

• just check
• just tauri-check
• just clippy