Feature: Chat layout toggle to reverse message sides (user right / assistant left)

[jeffscottward]

Summary

Add a chat layout option to reverse message sides: user on right, assistant on left.

Context

Requested preference for iOS-style conversational alignment.

Chat ref:

• 1470512265781313547

Expected Behavior

A toggle allows swapping message alignment sides for user vs assistant.

Acceptance Criteria

• Setting available in chat/session preferences.
• Layout updates immediately for active session.
• Preference persists across sessions/restarts.

cc @jeffscottward

[jeffscottward]

Implemented in PR #362.\n\nKey points:\n- adds persistent layout preference for message side alignment\n- wires setting through single-session and group-chat views\n- default behavior remains unchanged (user on right)\n\ncc @jeffscottward