Make a folder from the server browser

The in-app browser that chooses a library folder on the server could
only open folders that already existed, so a library, or an export
destination, that was not on the server yet had to be made in the
Nextcloud web page first. It now has "New folder": a name, then MKCOL,
then the parent listed again and the new folder walked into — a folder
somebody has just named is the one they mean to choose.

The listing is the server's rather than the name inserted locally: the
server may have normalised or refused it. A name with a slash, "..",
or nothing at all is refused before any request, because a folder
typed with a slash in it is a path the user did not mean.

remote_folders holds the two WebDAV round trips (list, make) off the UI
thread, with the answer delivered through a Slint timer, so the album
sheet can use the same browser.

ui/dr-ui/src/launch_ui.rs

@@ -342,6 +342,56 @@ fn wire_folder_picker_navigation(window: &AppWindow, controller: &Rc<LaunchContr
             render(&w, &ctl);
         });
     }
+    {
+        let weak = window.as_weak();
+        let ctl = controller.clone();
+        window.on_launch_browse_make(move |name| {
+            let Some(w) = weak.upgrade() else { return };
+            let (account, parent) = {
+                let m = ctl.model.borrow();
+                let Some(b) = m.browser.as_ref() else { return };
+                let Some(account) = m.session().cloned() else { return };
+                (account, b.path.clone())
+            };
+            let conn = match ctl
+                .store
+                .connection(&account, crate::remote::needs_secret(&account))
+            {
+                Ok(c) => c,
+                Err(e) => {
+                    ctl.model.borrow_mut().fail(format!("credentials: {e}"));
+                    render(&w, &ctl);
+                    return;
+                }
+            };
+            let name = name.trim().to_string();
+            let child = if parent.is_empty() {
+                name.clone()
+            } else {
+                format!("{parent}/{name}")
+            };
+            ctl.model.borrow_mut().browse_to(parent.clone());
+            render(&w, &ctl);
+            // Made, then walked into: a folder somebody has just named is
+            // the one they mean to choose.
+            let (weak, ctl) = (weak.clone(), ctl.clone());
+            crate::remote_folders::make(conn, parent, name, move |result| {
+                let Some(w) = weak.upgrade() else { return };
+                match result {
+                    Ok(_) => {
+                        ctl.model.borrow_mut().browse_to(child.clone());
+                        render(&w, &ctl);
+                        spawn_folder_list(w.as_weak(), ctl.clone(), child);
+                    }
+                    Err(e) => {
+                        ctl.model.borrow_mut().close_browser();
+                        ctl.model.borrow_mut().fail(e);
+                        render(&w, &ctl);
+                    }
+                }
+            });
+        });
+    }
     {
         let weak = window.as_weak();
         let ctl = controller.clone();