Add /clear command

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

server/src/api.rs

@@ -1128,6 +1128,13 @@ pub(crate) fn send_prompt(app: &AppState, session: crate::types::Session, text:
         tokio::spawn(do_compact(app.clone(), id.clone()));
         return Ok(json!({"ok": true, "command": "compact"}));
     }
+    if text == "/clear" {
+        if app.is_busy(&id) {
+            return Err(ApiError(StatusCode::CONFLICT, "session is busy".into()));
+        }
+        runner::clear_context(app, &id).map_err(|e| ApiError(StatusCode::INTERNAL_SERVER_ERROR, format!("{e:#}")))?;
+        return Ok(json!({"ok": true, "command": "clear"}));
+    }
     let cwd = PathBuf::from(&session.cwd);
     let root = app.root_for(session.owner_id.as_deref(), &cwd);
     let mut prompt_text = text.clone();