feat(native): P5-42 keep webview unthrottled in tray (instant background sync)

Add WebView2 additional_browser_args to disable Chromium background throttling
(--disable-background-timer-throttling / -renderer-backgrounding /
-backgrounding-occluded-windows) so the existing JS Matrix /sync loop and
notifications keep running full-speed when the app is closed to the tray, instead
of standing up a second headless Rust sync client. Tauri's default WebView2 args
are preserved (setting this overrides them). Windows/WebView2 only; does not block
system sleep (that's P5-46, calls-only). CI Windows compile pending.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -494,6 +494,15 @@ pub fn run() {
                 .visible(false)
                 .initialization_script(NOTIFICATION_BRIDGE)
                 .disable_drag_drop_handler()
+                // P5-42: keep the WebView2 renderer running full-speed while the
+                // app is closed to the tray, so the Matrix /sync loop and
+                // notifications aren't throttled/backgrounded by Chromium. Preserves
+                // Tauri's default WebView2 args (setting this overrides them) and
+                // appends the Chromium background-throttling disables. Windows-only
+                // in effect; harmless elsewhere. Does not block system sleep.
+                .additional_browser_args(
+                    "--disable-features=msWebOOUI,msPdfOOUI,msSmartScreenProtection --disable-background-timer-throttling --disable-renderer-backgrounding --disable-backgrounding-occluded-windows",
+                )
                 .on_page_load(|window, payload| {
                     if matches!(payload.event(), PageLoadEvent::Finished) {
                         let _ = window.show();