Fix draft message persistence between chatroom switches

[BP602]

Summary

Implements draft message persistence to resolve the issue where unsent messages are lost when switching between chatrooms.

Changes Made

• Draft Storage: Added draftMessages Map to ChatProvider state for per-chatroom draft storage
• DraftManager Component: Created component that automatically saves and restores draft content
• Auto-save: Draft content is saved on every editor change using Lexical update listeners
• Auto-restore: Draft content is restored when switching back to a chatroom
• Auto-cleanup: Drafts are cleared when messages are sent successfully
• Lexical Compatibility: Fixed node structure by properly using paragraph nodes for text content

Technical Implementation

• Built on top of PR Fix cross-platform icon compatibility #19 for cross-platform icon compatibility
• Uses Lexical's registerUpdateListener for real-time draft saving
• Integrates seamlessly with existing chat input architecture
• Maintains separate draft state for each chatroom independently

Test Plan

• Type a message in one chatroom without sending
• Switch to another chatroom
• Switch back to the original chatroom
• Verify the draft message is restored
• Send the message and verify draft is cleared
• Verify drafts work independently across multiple chatrooms

Fixes

Closes #23

🤖 Generated with Claude Code

[BP602]

Encountered issue where emotes (both 7tv and kick) restore as the name and not the image of the emote, but found the same happens on restore last message/arrow up, so will tackle in a separate issue.