feat: install found updates without waiting for a click

Where the app can replace itself (the portable exe and the AppImage), a check that finds a release now installs it and relaunches straight away. The .deb still only reports the update.

README.md

@@ -102,7 +102,8 @@ Grab `usage-monitor.exe` from the
 Put it in a folder of its own that you can write to (e.g.
 `%LOCALAPPDATA%\UsageMonitor\`) and run it. The app is portable: it keeps
 `settings.json` next to the exe, so moving the folder keeps your settings. It
-self-updates from the same Releases feed.
+updates itself from the same Releases feed: when a check finds a new
+release, it installs it and restarts on its own, with no click needed.
 
 **First-run note:** the binary is unsigned, so SmartScreen will show
 "Windows protected your PC". Click **More info** → **Run anyway**. Code
@@ -117,7 +118,7 @@ pick one:
 - `usage-monitor_X.Y.Z_amd64.AppImage`: make it executable
   (`chmod +x`) and run it. Like the Windows exe it is portable and keeps
   `settings.json` next to the AppImage file, so give it a folder you can
-  write to. The AppImage self-updates in place. If you turned on "Start
+  write to. The AppImage updates itself in place, the same way. If you turned on "Start
   at login" in v0.6.0 or earlier and the AppImage path contains a space,
   turn it off and on again once: those releases wrote the path unquoted,
   so the app never started at login.

src/runtime.rs

@@ -657,8 +657,9 @@ impl Runtime {
 
     /// Blocking body of [`Self::check_for_updates`]. Only a check that got
     /// an answer is stamped as the last check; a failed one leaves the
-    /// stamp alone and has the scheduler retry sooner.
-    fn run_update_check(&self) {
+    /// stamp alone and has the scheduler retry sooner. A release found where
+    /// the app can replace itself is installed straight away.
+    fn run_update_check(self: &Arc<Self>) {
         let proxy = update::proxy_url(net::env_proxy().as_ref(), self.http.system_proxy());
         let outcome = update::check(&self.ui.app, proxy);
         let succeeded = outcome.is_ok();
@@ -700,6 +701,13 @@ impl Runtime {
             succeeded,
         });
         self.refresh_shell(false);
+        let auto_apply = self.with_state(|s| {
+            s.update_status == UpdateStatus::Available && s.update_channel.can_apply()
+        });
+        if auto_apply {
+            log::info!("update found; installing it without waiting for a click");
+            self.apply_update();
+        }
     }
 
     /// Download and install the release the last check found on a worker