feat(mobile): add inline remove button for conversation participants

[salmonumbrella]

Summary

• Add inline X button to each participant row in the conversation actions panel
• Allows direct removal of participants without opening the "Add Participant" modal
• Uses existing CloseIcon (size 20) with hitSlop={16} for tap accessibility
• Reuses existing conversationParticipantActions.update() API

Changes

• AddParticipantList.tsx: Added remove button and handler
• ConversationActions.tsx: Pass conversationId prop

Test Plan

• Open a conversation with multiple participants
• Navigate to conversation actions (swipe right)
• Verify X button appears next to each participant name
• Tap X button on a participant
• Verify participant is removed and toast notification appears
• Verify participant list updates immediately

🤖 Generated with Claude Code

[salmonumbrella]

@muhsin-k — would you mind taking a look at this when you have a sec? It adds an inline remove button for conversation participants. Been open a couple months and I think it's a nice UX improvement. Thanks!