Implement basic foundations for SpaceLobbyScreen

[kevinaboos]

Addresses part of #645

First attempt at using claude/gemini for code generation, it sorta works but needed a lot of manual fix up.

Remaining TODO items:

• Save and restore the minimal UI state of the SpaceLobbyScreen: just which spaces are expanded. Use similar impl as RoomScreen.
  • We should probably move both the SpaceLobbyScreenUiState and the TimelineUiState into AppState, for faster/more efficient access to it, and also to be able to save/restore part of it to persistent storage.
• Fetch and query avatars using the avatar cache
• Display whether the room is marked as Suggested
• Display whether the room/space is joined already. If not, show a Join (or knock) button.
• Display the topic of the room/space
• In the top-level header, display whether the top-level space is Private or Public, how many members it has, and the topic
• Fix the room count in subspaces. It is off by one.
  • Hmm, apparently this is an SDK-level issue, and it's not always off by one, it's just not accurate.
• Optional: add a filter/search bar that filters the rooms and subspaces by name, ID, topic, etc.