Kill UiMessage variants replaced by state-driven rendering

sync_from_agent reads directly from agent entries, so remove:
- UserInput (pending input shown from MindState.input)
- ToolCall, ToolResult (shown from entries on completion)
- ToolStarted, ToolFinished (replaced by shared active_tools)
- replay_session_to_ui (sync_from_agent handles replay)

-139 lines. Remaining variants are streaming (TextDelta, Reasoning),
status bar state, or ephemeral UI messages (Info, Debug).

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/user/mod.rs

@@ -459,13 +459,10 @@ pub async fn run(
                 idle_state.decay_ewma();
                 app.update_idle(&idle_state);
 
-                // One-time: replay conversation after Mind init
+                // One-time: mark startup done after Mind init
                 if !startup_done {
                     if let Ok(ag) = agent.try_lock() {
-                        if !ag.entries().is_empty() {
-                            ui_channel::replay_session_to_ui(ag.entries(), &ui_tx);
-                            let _ = ui_tx.send(UiMessage::Info("--- restored from conversation log ---".into()));
-                        }
+                        // sync_from_agent handles conversation replay
                         let _ = ui_tx.send(UiMessage::Info(format!("  model: {}", ag.model())));
                         startup_done = true;
                         dirty = true;