tauri-app: 8b click-through notifications

OS notification body already arrived as a 'maarcadetweet:notification'
DOM event (Phase 7b). The toast pill that surfaces the body is now
clickable: left-click navigates to the URL the notification was
about (at://<did>/<col>/<rkey> opens the thread, unknown URL
falls back to the home view); right-click dismisses without
navigating. tauri-plugin-notification v2.x does not expose a
reliable OS-level notification-click callback (it only shows the
notification), so the two-step pattern (OS click focuses the app
+ in-app toast click navigates) is the standard workaround.

lastNotificationUrl is now $state so the toast title updates
when a new notification arrives.

.gitignore

@@ -17,7 +17,7 @@ Cargo.lock.bak
 crates/tauri-app/node_modules/
 crates/tauri-app/dist/
 crates/tauri-app/.svelte-kit/
-crates/tauri-app/.vite/
+.vite/
 crates/tauri-app/src-tauri/target/
 crates/tauri-app/src-tauri/gen/
 crates/tauri-app/src/assets/fonts/*.ttf