fix: skip app state restore after explicit logout

[TigerInYourDream]

Summary

Fixes #31.

This PR fixes the case where, after an explicit logout and then logging back into the same account, the Home area can still show stale UI from the previous session instead of starting from a clean state.

Root Cause

There were multiple pieces contributing to the stale UI during logout -> re-login:

1. The persisted AppState restore path could automatically restore the previous Home/dock workspace on the next login.
2. Some cached UI widgets, especially the room and space sidebars, still retained in-memory session state until fresh updates arrived.
3. Some timeline update send paths still used unwrap() and could panic if the receiver had already been dropped during logout/re-login races.

Fix

This PR applies three focused fixes:

• Skip automatic app-state restore once after explicit logout

  • When explicit logout reaches the point of no return, Robrix writes a per-user one-shot marker.
  • On the next login for that user, handle_load_app_state() consumes that marker and skips restoring the previous persisted Home/dock workspace.
  • Persisted local state is preserved on disk and is not deleted.

• Reset room and space widgets on logout

  • RoomsList and SpacesBar now clear their session-bound cached UI state when LogoutAction::ClearAppState is received.
  • This prevents stale room/space UI from flashing briefly before fresh data arrives.

• Avoid panicking when timeline receivers are dropped

  • Timeline update sends in pagination/member-loading paths no longer use unwrap().
  • If the receiver is already gone during logout/re-login, the update is dropped with a log message instead of panicking a Tokio worker thread.

Effect

• logout -> re-login no longer restores the previous Home/dock workspace automatically.
• Room/space sidebar UI is cleared during logout, reducing stale UI flashes on re-login.
• Dropped timeline receivers no longer cause SendError(..) panics during logout/re-login races.
• Persisted local state is preserved.
• Normal message syncing/loading is still allowed after re-login.
• account switch behavior is not intentionally changed by this fix.

Files changed

• src/logout/logout_state_machine.rs
• src/sliding_sync.rs
• src/persistence/app_state.rs
• src/home/rooms_list.rs
• src/home/spaces_bar.rs

Suggested verification

• Log in to an account, open some Home/dock content, logout, then log back into the same account. The old Home workspace should not be auto-restored.
• Verify the room/space sidebars do not briefly show stale data from the previous session before refreshing.
• Repeat logout -> re-login multiple times. Each cycle should start from a clean workspace.
• Verify that normal room/message loading still works after re-login.
• Verify that no SendError(..) panic occurs during pagination/member-loading while logging out or re-logging in.