desktop: reminders reach you when the window isn't in front

A Rust worker reads due reminders from the local store every 15 s and
announces each occurrence once: always to the main window as a toast, and
as a system notification (tauri-plugin-notification) when that window
isn't focused. The page no longer polls on the desktop; its Notification
went nowhere in WebKitGTK and its timer stopped with the window. The
Reminders page says what each surface actually does.

Core gains store::due_reminders, compared by instant, not by string.

Refs #5171

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

desktop/src-tauri/src/lib.rs

@@ -14,6 +14,7 @@ mod capture;
 mod commands;
 mod crossover;
 mod integration;
+mod reminders;
 mod update;
 
 /// The build a PERSON reads, baked in by the desktop lane at compile time.
@@ -87,6 +88,8 @@ pub fn run() {
         // `setup`, once the store is open and can be asked which one to use — the
         // plugin only has to exist before then.
         .plugin(tauri_plugin_global_shortcut::Builder::new().build())
+        // System notifications for due reminders, raised by the `reminders` worker.
+        .plugin(tauri_plugin_notification::init())
         // Attachment bytes are served to the webview from the local blob store
         // (M10.7f). Registered on the BUILDER because a scheme has to exist before
         // the webview is created; the directory it reads from arrives later, in
@@ -146,6 +149,9 @@ pub fn run() {
             // Last: the worker reads the store and the blob store, both managed now.
             // Its first cycle is the launch sync.
             autosync::start(app.handle())?;
+            // Announces due reminders from the store, including while the window is
+            // minimised or covered.
+            reminders::start(app.handle())?;
             // Coming back to the window is when someone is about to look, so it asks
             // for a cycle. Rate-limited in autosync, because focus flaps constantly.
             if let Some(window) = app.get_webview_window("main") {