feat(desktop): show the installed app's own version in the UI

Nothing displayed which desktop build was actually installed — debugging
a stuck update meant inferring the current version backwards from the
update prompt's target version. Added DesktopVersionBadge (next to the
existing server-side VersionBadge) using @tauri-apps/api's getVersion(),
the real running app version baked in from tauri.conf.json. No-ops in a
browser. Exported inTauri() from origin.ts instead of redefining it again.

pnpm-lock.yaml

@@ -108,6 +108,9 @@ importers:
       '@tanstack/react-router':
         specifier: ^1.170.16
         version: 1.170.16(react-dom@19.2.7(react@19.2.7))(react@19.2.7)
+      '@tauri-apps/api':
+        specifier: ^2.11.1
+        version: 2.11.1
       '@tauri-apps/plugin-http':
         specifier: ^2.5.2
         version: 2.6.0