UI: update notice, Help › Check for Updates and Reinstall, Settings › Updates (#231)

The window checks at start-up at most once a day when automatic checks are on (Settings and
the first run's question), never while that question is open and never without a host, so the
browser and tests make no network call. A newer release shows a quiet notice in the status bar
("FieldCraft X is available — What's new · Install · Skip"); Install downloads and verifies
through the host, then asks to restart, saving or asking about unsaved changes first, and the
host swaps the release in after the window closes. A .deb/.rpm install offers the system's
installer and the command instead. Skip this version is kept in the preferences.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/ui-egui/src/appbar.rs

@@ -340,10 +340,23 @@ fn help_menu(app: &mut ModelApp, ui: &mut egui::Ui) {
         .button("Report a Bug…")
         .on_hover_text("Draft a GitHub issue with the version, the OS and the last error; nothing is sent until you submit it")
         .clicked();
-    let settings = ui.button("Settings…").on_hover_text("Privacy: anonymous usage sharing").clicked();
+    let (mut check, mut reinstall) = (false, false);
+    if app.updates_available() {
+        check =
+            ui.button("Check for Updates").on_hover_text("Ask GitHub Releases whether a newer FieldCraft is published (app.update.check)").clicked();
+        reinstall = ui
+            .button("Reinstall FieldCraft…")
+            .on_hover_text("Download this version again, verify it and swap it in, to repair a damaged install")
+            .clicked();
+    }
+    let settings = ui.button("Settings…").on_hover_text("Privacy and updates").clicked();
     ui.label(egui::RichText::new(format!("FieldCraft {}", crate::VERSION)).color(t.text_dim));
     if report {
         app.report_bug(None);
+    } else if check {
+        app.check_for_updates();
+    } else if reinstall {
+        app.reinstall();
     } else if settings {
         app.open_settings();
     }