Rust no message

Introduce a controlled message input and client-side send flow, and rename the DB save function.
- Add message_input field to AppState in client and server-initialized state so the UI can hold draft messages.
- Implement a controlled Input in event_list: update AppState on input events, build and sign a Message event, and post it asynchronously; clear the input after sending. Replace direct DOM lookup with state-driven value.
- Update server handler to initialize message_input in the served AppState.
- Rename db function save_create_account_event -> save_event and update its call site in main.rs.
- Minor cleanup: unused EventHandler parameters renamed to _set_state in login/create dialog handlers.
These changes enable composing and sending message events from the UI and align the server DB API naming. Follow-up: ensure db::save_event implementation persists message events as intended.